Abstract Introduction Heterotopic Ossification (HO) is a benign process of osseous matrix deposition in extra-skeletal tissues; it is well recognised in the orthopaedic setting, especially after blast injury, but is a rare phenomenon following abdominal surgery and is likely under reported. The aetiology is unclear but may be due to differentiation of local mesenchymal cells into osteoblasts leading to calcification of the extracellular matrix, or damage to xiphoid or pubis causing liberation of bone-forming cells into the wound. Case Report A 46-year-old man, presented with perforated diverticulitis and underwent an emergency Hartmann's procedure with temporary abdominal closure. Sequential returns to theatre failed to achieve fascial closure and he was managed as a laparostomy. Two years later he underwent reversal of Hartmann's with complex abdominal wall reconstruction (CAWR) – the procedure was complicated by an unrecognised ring of HO around the edge of his laparostomy wound, which necessitated additional excision of fascia. Only partial fascial closure could be achieved leaving an 8×4cm bridge over polypropylene mesh. After a complicated post-operative course, he was discharged home with intestinal continuity and healed abdominal wounds. Discussion Pre-operative review of the 2-D axial CT images failed to identify the almost complete ring of HO clearly evident on 3-D reconstructions which impacted on the outcome of the CAWR; 3-D reconstructions should be routinely reviewed. It is commoner in males, those with prolonged ICU intubation, hollow viscus injury and non-closure of the fascia. Restoration of intestinal continuity can be safely performed with complex abdominal wall reconstruction.