BACKGROUND Urachal cyst is one of a spectrum of urachal abnormalities most commonly found in children. They are very rarely seen in adults because the urachus is normally obliterated in early infancy. METHODS We describe a case of a 32 year old male Caucasian who presented with a tender, midline, infraumbilical mass and purulent umbilical discharge. Diagnosis of an infected urachal cyst was confirmed on magnetic resonance scan. He was treated initially with broad spectrum antibiotics in order to allow sepsis to resolve prior to surgical excision of the cyst and fibrous tract. Cystoscopy was performed intraoperatively to exclude sinus communication with the bladder. Histology of the excised specimen showed chronic inflammation with no evidence of malignancy. Postoperative recovery was uneventful. CONCLUSIONS Urachal abnormalities are rare in adults. Clinical presentation is non-specific; therefore, a high index of suspicion is required in order to make the diagnosis. When diagnosed, surgical excision is advised because of the risk of malignant transformation.