Three cases of urachal abscess with extensive interstitial inflammation and fibrosis are reported. Clinically, all patients had a lower abdominal mass and CT scan and ultrasonic examination revealed a large tumour located anterior or superior to the bladder. They all underwent laparotomy and had either a partial cystectomy or an en bloc resection of the bladder and adjacent organs due to severe adhesions. Microscopic examination of the specimens revealed no evidence of carcinoma and only abscess formation with extensive chronic interstitial inflammation and fibrosis were seen. In one case, residual columnar epithelium suggestive of urachal origin was identified in the abscess cavity. Urachal abscess should be considered when dealing with lower abdominal masses.