Purpose: Intracavitary (IC) delivery of cisplatin (CDDP) has been used in the treatment of a variety of adult malignancies based on the favorable pharmacokinetics obtained locally. Since IC CDDP has not been reported in children, we studied its use in a group of pediatric patients with regard to safety, toxicity, pharmacokinetics, and responses. Patients and Methods: Eleven patients with an age range of 8 months to 21 years with diagnoses of rhabdomyosarcoma (n = 5), pleuropulmonary blastoma (n = 2), osteosarcoma (n = 2), Ewing's sarcoma (n = 1), and malignant rhabdoid tumor of the kidney (n = 1) were studied. Eight patients received intrapleural (IPL) CDDP and three received intraperitoneal (IP) CDDP, either at diagnosis (n = 3) or relapse (n = 8), for malignant pleural effusion (n = 3), malignant ascites (n = 2), pleural-based tumor (n = 4), pulmonary metastases (n = 1), or abdominal tumor spillage (n = 1). Results: IC CDDP was well tolerated by pediatric patients. Two patients experienced a transient increase in serum creatinine levels (> two times baseline) and two patients experienced severe neutropenia (absolute neutrophil count < 500/μL). Pharmacokinetic measurements showed a 40-fold advantage for the pleural cavity versus serum after IPL CDDP and serum levels comparable to those achieved with systemic administration of CDDP. Four of five patients who received IC CDDP for malignant ascites or pleural effusion had at least a temporary response. Only three of 11 patients studied had local recurrences following IC CDDP. There are currently four survivors in the study group, including two long-term survivors at greater than 8 years since IPL CDDP treatment. Conclusion: The safety, toxicity, and pharmacokinetics of IC CDDP in pediatric patients are similar to that reported in adult patients. The low incidence of local recurrence following IC CDDP in this group of largely relapsed patients suggests that further study of IC CDDP far pediatric patients is warranted.