The prognosis for pulpotomy of primary molars with calcium hydroxide as wound dressing was evaluated clinically and radiographically. Thirty-three primary mandibular molars were amputated under the following conditions: (1) chronic coronal pulpitis, (2) the amputation was done with diamond instruments and a high-speed machine under aseptic conditions, and (3) application of calcium hydroxide in contact with the wound surface. After 1 year the treatment was regarded as successful for 22 of the teeth (67%); 11 teeth showed internal dentin resorption. After 2 years the frequency of success, allowing for drop-out, was 59%. Internal dentin resorption was seen in 14 root canals; in 10 of them within the first 6 months. A histologic study of nine root pulps with internal dentin resorption revealed an extra-pulpal blood clot on the wound surface in five.