AIM: Constipation studies have only evaluated behavioural difficulties in children with faecal incontinence. This study evaluated changes in behavioural difficulties in childhood with functional constipation (FC) with and without faecal incontinence, based on treatment outcomes. METHODS: Children aged five to 16 years who fulfilled the Rome III criteria for FC received conventional treatment. The Strength and Difficulties Questionnaire was completed at inclusion and at the 12-month follow-up. RESULTS: We included 116 children. The behaviour scores decreased in successfully treated boys (10.3 versus 7.9; p < 0.001) and girls (10.0 versus 7.4; p = 0.0001) with and without faecal incontinence. There was no decrease in the behaviour scores in children with unsuccessful outcomes. Unsuccessfully treated boys had significantly higher behaviour scores than successfully treated boys at inclusion (13.2 versus 10.3; p = 0.006) and after 12 months (11.4 versus 7.9; p = 0.02). No difference was found between unsuccessfully treated and successfully treated girls at inclusion (10.5 versus 10.0; p = 0.77) or after 12 months (10.3 versus 7.4; p = 0.18). CONCLUSION: Our findings indicate that conventional treatment of FC had a positive impact on behavioural difficulties in constipated children with and without faecal incontinence. This study highlights the importance of proactive detection and treatment of FC in paediatric patients.