In an effort to critically define the incidence and clinical characteristics of secondary responses to cisplatin-based therapy in patients with ovarian cancer previously treated with a cisplatin-based program, a retrospective review was undertaken of patients at the Memorial Sloan-Kettering Cancer Center who received greater than or equal to two cisplatin/carboplatin-based programs. Eighty-two patients were identified who met the entry criteria of having had a cisplatin-free interval (CFI) of more than 4 months between the completion of their first regimen and the institution of a second cisplatin/carboplatin program. Of the 72 assessable patients (10 had no measurable disease, and a laparotomy was not performed to assess response), 31 (43%) responded, including 10 surgically defined complete responses (S-CRs). The overall response rates (and S-CR rate), based on duration of CFI, were 5 to 12 months, 27% (5%); 13 to 24 months, 33% (11%); and more than 24 months, 59% (22%). Twenty-nine patients (35%) received noncisplatin/carboplatin-containing treatments between the cisplatin programs. Patients without any treatment for more than 24 months from the completion of their initial therapy experienced a 77% (17 of 22) response rate and a 32% (seven of 22) S-CR rate. In conclusion, secondary responses to cisplatin/carboplatin-based treatment are common in patients with ovarian cancer who have previously responded to the agents and increase in frequency with greater distance from the initial therapy.