We analysed the prevalence of cigarette smoking among subsequent birth cohorts of Spanish males and females. Data were drawn from the Spanish NHIS conducted in 1993 ( = 26 400), 1995 ( = 8300) and 1997 ( = 8300). From the original computer files, the three surveys were pooled to obtain a single sample. A total of 33 223 subjects (16 036 men and 17 187 women) born between 1900 and 1979, >/= 16 years old, were directly interviewed and with complete information on the history of smoking included for analysis. Based on each respondent's sex and calendar year of birth, the person was classified into a particular sex-birth cohort in the decades from 1900-09 to 1970-79. For each year from date of birth to date of survey, respondents were further classified as either cigarette smoker or nonsmoker. The prevalence of cigarette smoking among successive cohorts of Spanish men and women was estimated, with correction for excess mortality of smokers. In men, the peak in smoking was reached in the 1950-59 birth cohort (prevalence rate of 68% at ages 20-29), after increases during the previous calendar years. Smoking among women was rare until 1960. Female smoking prevalence rates increased progressively among subsequent cohorts until 1980. The age distribution of smoking prevalence in women in 1990 mimics that observed in men 40 years earlier. A substantial delay in the spread of the tobacco epidemic among men is apparent. In women, the delay in the initiation of the smoking epidemic ended with a quick diffusion of the habit.