Ganciclovir is a nucleoside guanosine analogue that exhibits therapeutic activity against human cytomegalovirus infection, and is primarily excreted via glomerular filtration and active tubular secretion. The adverse effects induced by ganciclovir therapy are generally of a hematological nature and include thrombocytopenia and leukopenia. Low marrow cellularity and elevated serum creatinine have been identified as risk factors for ganciclovir-induced neutropenia. However, the risk factors for thrombocytopenia have yet to be determined. Therefore, this study investigated patients administered ganciclovir to determine the risk factors for thrombocytopenia and leukopenia. Thrombocytopenia occurred in 41 of these patients (30.6%). Multivariate logistic regression analysis identified three independent risk factors for thrombocytopenia: cancer chemotherapy (odds ratio (OR)=3.1), creatinine clearance (<20 mL/min) (OR=12.8), and the ganciclovir dose (≥12 mg/kg/d) (OR=15.1). Leukopenia occurred in 36 patients (28.6%), and white blood cell count (<6000 cells/mm(3)) (OR=3.7) and the ganciclovir dose (≥12 mg/kg/d) (OR=7.8) were identified as risk factors. These results demonstrated that several factors influenced the occurrence of ganciclovir-induced thrombocytopenia and leukopenia, and suggest that special attention should be paid to patients receiving cancer chemotherapy with a low creatinine clearance (<20 mL/min) and high dose (≥12 mg/kg/d) in order to avoid ganciclovir-induced thrombocytopenia.