Appendicular osteosarcoma was diagnosed in 30 dogs. Fifteen dogs were treated by limb amputation alone, and 15 dogs were treated by limb amputation followed by 2 doses of cisplatin given IV approximately 2 and 7 weeks after limb removal. Mean survival time after limb amputation alone +/- SD was 190 +/- 138 days (median, 168 days); 7 dogs survived longer than 6 months, and 3 dogs survived more than 1 year. Fourteen of 15 dogs treated by amputation and administration of cisplatin survived a mean of 315 +/- 158 days (median, 290 days) after amputation, and 1 dog was still alive at 1,095 days; 13 dogs survived longer than 6 months and 5 dogs survived more than 1 year. Survival time was significantly (P less than 0.05) greater in dogs given cisplatin.