The aim of the study was to determine the date of regular ovulation after the menarche to better understand the physiology of female adolescence, especially as it pertains to the use of hormonal contraception. Early morning urine samples were collected from 51 girls in the perimenarche for 9 weeks semi-annually during 2 years. Estrone- and pregnanediol-3-glucuronide values were determined. Cycles lasting 35-40 days at the onset of menses shortened to 28 days after the 23rd-25th cycle. Menses reached a 5.0-5.5 day average length at about the same time. After the 20th cycle, ovulation could be demonstrated in more than 50% of the study patients. Using a scoring system, regular ovulation could be expected on the basis of somatic data with scores of greater than 16. Hormonal contraception may be prescribed 2 years after the menarche, based on scores of greater than 16 and ovulation proven be hormonal cytology and basal body temperature.