Case A healthy 11-year-old female presented to accident and emergency (A&E) with a two-month history of constipation and progressive abdominal pain. She had previously seen her General Practitioner (GP) with no improvement. In A&E she was treated and discharged by a paediatrician; a presumptive diagnosis of constipation was still made. Two days later she re-presented with worsening pain, anorexia and "pelvic pressureâ€ on passing urine. She was seen by a paediatric consultant who identified a three-month history of cyclical abdominal pain and primary amenorrhoea despite normal development of secondary sexual characteristics. Evidence of a pelvic mass prompted a gynaecological referral. The gynaecology team confirmed a soft abdomen with a 16 week size left-sided pelvic mass. A bulging blue-grey membrane was seen at the vaginal introitus. A clinical diagnosis of haematocolpos secondary to an imperforate hymen was made. Trans-abdominal ultrasound scan confirmed a large haematocolpometra (111 x 87 x 77mm). Hymenotomy under general anaesthesia was performed, draining 600mls of dark blood/clots. The patient made an excellent post-operative recovery with prompt resolution of symptoms. A 3 month post-operative pelvic MRI excluded other urogenital tract anomalies. Background Imperforate hymen has a prevalence of 0.014-0.1%1. It causes haematocolpos and associated haematocolpometra/haematosalpinx in 90% of cases2. Usually asymptomatic till puberty, it classically presents as primary amenorrhoea, cyclical abdominal pain (60%) and urinary retention (58%)2. Associations are reported with back pain, lumbo-sacral radiculopathy3 and an acute abdomen following rupture of a haematosalpinx4. Constipation is a common childhood disorder which can affect 30% of children worldwide5; most cases are of functional aetiology6. Differential diagnoses include metabolic disorders, drugs, anatomical or neurological abnormalities of the colon or spinal cord. Constipation also occurs in 20-27% of imperforate hymen patients1. NICE guidance5 does not mention any obstructive reproductive tract anomalies as a cause for childhood constipation. Conclusion This case highlights important learning points: GPs, A&E doctors and paediatricians should consider haematocolpometra as a differential diagnosis in pubertal patients presenting with constipation and a pelvic mass. A comprehensive review of systems and gynaecological assessment was essential to successfully manage this patient.