The power of the association between oral contraceptives and cervical cancer was analysed in all the papers published up to date. Fifty-three publications (from 48 studies) wer collected and graded as to quality using meta-analytical methods. Power achieved a figure of greater than or equal to 0.8 in a 24% of the associations studied. It showed a significant relationship with the existence of a significant relative risk of the oral contraceptives for cervical cancer, with the quotient between sample sizes of reference and index groups, and with the sample size of a study, although the relationship was not linear to these two latter variables. Power did not show any significant relationship to other variables related to the design of a study, or to the biases detected. Logistic regression analysis included as predictors of a power greater than or equal to 0,80 the existence of a significant relative risk and the use of adjusted relative risk.