OBJECTIVES: The effect of caffeine consumption on fertility was examined prospectively in 210 women. METHODS: Women reported on caffeinated beverage consumption and pregnancy status monthly. Odds ratios for becoming pregnant were calculated for both high and moderate vs low consumption. RESULTS: No significant association was found for any of the caffeinated beverages except tea. Drinking one-half cup or more of tea daily approximately doubled the odds of conception per cycle. CONCLUSIONS: These data suggest that caffeine may not be the responsible agent for variation in fertility associated with consumption of the beverages examined.