TOKYO — The popularity of Nintendo's Wii videogame console and DS portable game machine has propelled the Japanese company's shares to records in recent years. But it could be Game Over for such big returns in the future.

Nintendo, which was written off as a has-been a few years ago, has had a phenomenal run, overshadowing Sony's PlayStation with two successful devices that have taken the world by storm.

While Tokyo's benchmark Nikkei Stock Average of 225 companies has fallen nearly 25 percent in the past two years, Nintendo's stock price has tripled. When the company reports earnings April 24 for the year ended March 31, the results are expected to show similarly strong growth in profit and revenue.

Nintendo, with 3,300 employees and annual revenue of about $16 billion, has become Japan's third-largest company by market capitalization, vaulting past some big names, such as mobile-phone operator NTT DoCoMo, auto maker Honda Motor and electronics conglomerate Matsushita Electric Industrial.

Most analysts are still bullish about Nintendo, with "outperform" or "buy" investment ratings. But some believe the days of such heady growth are coming to an end, particularly with more signs of a recession looming in the U.S., its biggest market.

A stronger yen also diminishes the value of Nintendo's overseas profits when converted into its home currency.

"They're at the top of their game at the moment, but it's not going to be easy to keep performing at levels that exceed people's expectations," says Hiroshi Kamide, an analyst for KBC Securities. Last month, he downgraded the company to "hold" from "buy" and cut his 12-month price target to 57,500 yen ($570.05) from 82,500 yen.

Although Nintendo has held up better than most Japanese stocks in the recent downturn, its share price has fallen 16 percent in 2008, and the stock has been fluctuating between 50,000 yen and 70,000 yen since last autumn. Monday, the shares rose 0.7 percent to 55,900 yen.

Analysts say they believe Nintendo's business will continue to be strong. Wii is still outselling Sony's PlayStation3 and Microsoft's Xbox360, and retailers are having trouble keeping the consoles on store shelves. Nintendo has forecast sales of 18.5 million of the consoles in the just-ended fiscal year, compared with Sony's expectations for 9.5 million in PS3 sales.

Analysts estimate Nintendo will sell an additional 26 million consoles in the current fiscal year as it increases production.

Nintendo also is releasing some big game titles this spring. Mario Kart Wii, a racing game featuring the popular characters, is being launched world-wide this month. The much-anticipated Wii Fit exercise game, which is played on a device that resembles a bathroom scale, will be launched in the U.S. and Europe in the next month. Wii Fit came out in December in Japan to great success. Wii Music is expected to come out this year. All three are expected to sell well.

Still, after high-double-digit and triple-digit growth in sales and profit since the launch of the DS portable game device in November 2004, expectations on the company have risen significantly even though it becomes more difficult to continue to make those kinds of strides.

Nintendo's operating profit is expected to have doubled to 460 billion yen for the just-ended fiscal year. For the current year, though, analysts on average expect it to grow 20 percent to about 550 billion yen.

If foreign-exchange rates stay at current levels, that also would hurt Nintendo, which gets nearly 39 percent of its revenue from the U.S. Since the beginning of 2008, the U.S. dollar has fallen to about 101 yen from 112 yen.

A continually weaker dollar "could change the company to a single-digit growth company," says Jay Defibaugh, an industry analyst for Credit Suisse Securities. In his view, the yen is proving stronger this year than what many analysts assumed. His own exchange-rate assumption is 106 yen. Mr. Defibaugh has a "hold" rating on Nintendo with a 12-month price target of 57,000 yen.

The videogame industry is generally considered "recession-proof" because people spend more time at home in a downturn, and games are a relatively inexpensive form of entertainment.

Still, Mr. Kamide of KBC says he is concerned about a U.S. economic slowdown's effect on Nintendo. A big part of Nintendo's growth has been expanding the market itself by targeting new categories of users such as women and senior citizens, and he believes they are more likely to give up games than serious game players are if they are strapped for cash.

Some analysts believe sales of the DS portable game device, which has seen tremendous growth since its launch, are peaking, particularly in Japan, which has driven much of the demand. The company has estimated world-wide sales of 29.5 million units for the year ended March.

It won't be long before a big talking point about Nintendo will be its future and what kind of devices it will make.

"If shares are going to move up, they'd better move before the next 18 months, when we start obsessing about what the next-generation machines will look like," Mr. Defibaugh says. "They have huge comparisons to overcome," he added, referring to the Wii and DS.

Wii Fit exercise game, which is played on a device that resembles a bathroom scale

man... (mumbles and grumbles) wii (grumbles and mumbles) outsales sony. Everyone really ended up liking it's gimmicky nature.

And what's more, it makes all the surface buttons unreachable. You can really only play Umbrella Chronicles and that Zelda shooter. Every other games you'll need quick access to the A button and directional buttons.