Recently, the use of platinum-containing antineoplastic agents for extended periods has increased. In this study, we determined the relationship between the hypersensitivity reactions to cisplatin or carboplatin and the frequency of administration among patients with thoracic malignancies. The study included 255 patients with thoracic malignancies who were treated with chemotherapy containing cisplatin or carboplatin in our institution between April 2007 and October 2008. A total of 89 patients received a median of 3 courses of cisplatin and 140 patients a median of 4 courses of carboplatin. A median of 6 courses of cisplatin plus carboplatin was administered to a further 26 patients. The total incidence of hypersensitivity reactions was 1.96%. Patients who were treated with <6 courses of platinum-containing antineoplastic agent did not experience any hypersensitivity reaction, but one patient, who was administered with 6 courses of platinum-containing antineoplastic agent experienced a hypersensitivity reaction (0.44%), as did four patients who were administered ≥7 courses (13.8%). Univariate and multivariate analyses indicated that the number of courses of platinum-containing antineoplastic agents was significantly correlated to the incidence of hypersensitivity reactions to these agents.