The purpose of this study was to assess the pattern and significance of tumour calcification in ovarian carcinoma. Patients with calcifying ovarian carcinoma were identified from radiological reports. Their tumour characteristics, serum calcium levels, treatment and survival were compared with a control group of patients with non-calcifying disease. Patterns and distribution of calcification were assessed. Available serial CT scans were reviewed for changes in both soft-tissue and calcified disease according to RECIST (response evaluation criteria in solid tumours) criteria where feasible. Temporal changes in calcification were correlated with changes in soft tissue disease and CA125 levels. The calcified group numbered 122 (22 other patients had calcifying tumour but insufficient clinical data). Calcification in ovarian carcinoma had a prevalence of 8% (144/1721) in our series. There was a significant difference (p<0.001) between the two groups in the distribution of histological type, with serous tumours being more common in the calcified group (74/122 (61%)) than in the controls (509/1498 (34%)). The calcified tumour patients tended to have lower grade disease (p<0.001). No differences between the groups were found for age, treatment or serum calcium levels. Distribution of calcification was diffusely peritoneal in 34 patients, in association with a pelvic mass in 15, nodal in 11 and within the anterior abdominal wall in 2. There was no correlation between changes in calcification on serial CT scans and corresponding CA125 levels. In conclusion, calcification tends to occur most commonly in serous cystadenocarcinomata and in tumours of lower grade. Changes in calcification cannot be used as a marker of disease response.