ObjectivesTo establish whether long-term use of melatonin influences pubertal development, sleep quality and mental health development in children as compared with the normal Dutch population of the same age.MethodsThis follow-up research study was conducted in children included in a previous melatonin dose-finding trial. Outcomes were measured using questionnaires (Strength and Difficulties Questionnaire (SDQ), Children's Sleep Habits Questionnaire (CSHQ) and Tanner Stages) adopted for Dutch children. Mean duration of therapy, persistence of effect, adverse events and (other) reasons leading to cessation of therapy were additional objectives of this study.ResultsMean years of usage (n = 51) was 3.1 years (min 1.0 year, max 4.6 years), mean dose 2.69 mg (min 0.3 mg, max 10 mg). Mean SDQ score, mean CSHQ score and Tanner Stages standard deviation scores did not differ in a statistically significant way from published scores of the general Dutch population of the same age and sex.ConclusionsThis follow-up study demonstrates that melatonin treatment in children can be sustained over a long period of time without substantial deviation of the development of children with respect to sleep quality, puberty development and mental health scores, as compared with the general Dutch population.