OBJECTIVE: To assess sperm production and aneuploidy in Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL) before and after treatments. DESIGN: Multicenter, prospective, longitudinal study of lymphoma patients analyzed before treatment and after 3, 6, 12, and 24 months. SETTING: University hospitals. PATIENT(S): Forty-five HL and 13 NHL patients were investigated before and after treatment. Treatment regimens were classified in two groups: ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) with or without (+/-) radiotherapy, and CHOP (doxorubicin, cyclophosphamide, vincristine, prednisone)/MOPP-ABV (mechlorethamine, oncovin, procarbazine, prednisone-doxorubicin, bleomycin, vinblastine). A control group of 29 healthy men was also studied. INTERVENTION(S): Semen analyses and aneuploidy study by FISH were performed at each time point. MAIN OUTCOME MEASURE(S): Comparison of mean sperm characteristics and percentage of sperm aneuploidy rates before and after treatment. RESULT(S): Before treatment, HL and NHL men had altered semen characteristics and higher sperm aneuploidy rates (median 0.76 [interquartile range 0.56-0.64]) than the control group (0.54 [0.46-0.74]). After treatment, sperm production was significantly lowered 3 and 6 months after ABVD +/- radiotherapy or CHOP/MOPP-ABV. After ABVD +/- radiotherapy, the aneuploidy rate increased significantly only at 3 months, and values obtained 1 or 2 years later were lower than pretreatment values. In contrast, in the CHOP/MOPP-ABV treatment group, semen characteristics and aneuploidy rate did not return to normal levels until 2 years after treatment. CONCLUSION(S): Lymphoma itself has consequences on sperm aneuploidy frequency before treatment. Moreover, lymphoma treatments have deleterious effects on sperm chromosomes related to treatment type and time since treatment. Patient counseling is essential concerning the transient but significant sperm aneuploidy induced by lymphoma and its treatments.