Objective To investigate oligomenorrhoea in adolescents with type 1 diabetes and the possible relationship with glycaemic control. Study design The study group consisted of 81 female adolescents with type 1 diabetes whose mean age was 15.0 years (range 12–18). The control group consisted of 205 healthy adolescents with a mean age of 15.5 years (range 12–18). Data on menstruation were collected by two parallel self-administered questionnaires. Oligomenorrhoea was defined as having a menstrual cycle longer than 36 days throughout the past year (5–6/year). The metabolic control of diabetes was evaluated by calculating the mean value of HbA1c during the past year. Results Age of menarche was greater for adolescents with type 1 diabetes (12.2 ± 1.4 vs. 11.7 ± 1.2, p < 0.000) compared to healthy age-matched controls. Logistic regression analysis with oligomenorrhoea as the dependent binary variable revealed an odds ratio equal to 7.8 (95% CI 3.411–17.853) for adolescents with type 1 diabetes (p < 0.000). Finally, a second logistic regression analysis, concerning only adolescents with type 1 diabetes and with the same binary variable, estimated an odds ratio of 4.8 (95% CI 1.784–13.057, p < 0.002) for HbA1c, and an odds ratio of 5.3 (95% CI 1.821–15.130, p < 0.002) for the frequency of hypoglycaemia. Conclusion In adolescents with type 1 diabetes, menarche occurs later and oligomenorrhoea is more frequent. The relative risk of having oligomenorrhoea is greater when there is an increased value of HbA1c or when hypoglycaemia is more frequent.