Maternal overweight and obesity in pregnancy has been associated with earlier age of menarche in daughters as well as reduced semen quality in sons. We aimed at investigating pubertal development in sons born by mothers with a high body mass index (BMI). The study included 2522 sons of mothers that during pregnancy in 1984-1987 were enrolled in a mother-child cohort and gave information on their pre-pregnancy height and weight from which we calculated their BMI. Information on sons' pubertal development, assessed by age when starting regular shaving, voice break, acne and first nocturnal emission, was obtained from web-based questionnaires in 2005, when sons were 18-21 years old. Multiple linear regression analyses showed that sons of obese mothers on average started to shave regularly 8.3 (95% confidence interval: 2.5-14.0) months earlier than sons of normal weight mothers. For the three other indicators of pubertal development, results also indicated earlier pubertal development among sons of obese mothers. After excluding sons of underweight mothers in a subanalysis, we observed an inverse trend between maternal pre-pregnancy BMI and age at regular shaving, acne and first nocturnal emission. In conclusion, maternal pre-pregnant obesity may be related to earlier timing of pubertal milestones among sons. More research, preferably based on prospectively collected information about pubertal development, is needed to draw firm conclusions.