The objectives of this study were to determine if a seasonal trend exists in adolescent pregnancies and to compare the teen conception rate per month to an adult population.The study was conducted in a tertiary care Canadian hospital that has a one-site model of care.A retrospective chart review of all adolescent pregnancies over a 5-year period (N = 838) was undertaken. From the 13,554 adult pregnancies over the same time period, a random sample of 838 pregnancies was chosen for similar chart review. A chi-square test was used to compare the proportion of pregnancies conceived in each calendar month between the two groups.Pregnancies ending in spontaneous abortions, elective terminations, ectopic pregnancies, as well as obstetrical deliveries, were included.There was a significantly different monthly trend seen in adolescent pregnancy conceptions when compared with the adult group (χ² = 24.38, df = 11, P = 0.0112). The adolescent group was observed to have a unique peak in the number of pregnancies conceived in March (10.5% of pregnancies conceived compared to 7.3% in adults). In addition, 8.5% of conceptions in adolescents occurred in December compared to 10.4% in adults.There are several plausible explanations for the modest but real differences identified in this study including trends in fecundity/fertility or social/school events that lead to increased sexual activity. Peaks in conception indicate times when a greater need for health care services exists, and when preventive education can be most effective.