Malignant transformation of benign ovarian cystic teratomas has been reported in 0.5 to 2% of cases. Many different types of cancer can develop, including squamous cell carcinoma, which is by far the most frequent (75%). The mean age of diagnosis is over 50 years. Minimal surgical techniques have been increasingly popular and laparoscopic removal of benign ovarian cysts has become common practice. Malignant transformation is rare but needs to be recognized in order to avoid dissemination of malignant cells during surgery. Direct invasion of the adjacent pelvic structures and small intestine represents the most common mode of spread. Survival is not improved by post-operative radiotherapy or adjuvant chemotherapy in patients with extracapsular disease. We report two cases, one of which presented with spontaneous ovarian abscess and paraneoplastic hypercalcemia.