Background. Characterization of the incidence of posttransplant lymphoma over time may help guide the timing and intensity of posttransplant monitoring. We analyzed the United States Renal Data System to describe the occurrence of lymphoma following renal transplantation. Methods. All end-stage renal disease patients placed on the transplant waiting list between January 1, 1990 and December 31, 1999 were considered. Survival analysis was used to estimate lymphoma risk in renal transplant patients. Results. Of 89,260 eligible patients, a total of 556 lymphoma cases were identified with 357 in transplant patients. The overall rate of posttransplant lymphoma was 33.3/10,000 person-years in transplant patients. There was variation in the duration and magnitude of increased lymphoma risk by age. The highest rates of lymphoma were among transplanted patients in the first 12 months, after which the rate of lymphoma decreased. Among Caucasian transplant recipients less than 25 years of age, the adjusted relative risk of lymphoma ranged from 13.82 [95% CI: (3.96, 48.15)] within 6 months posttransplant to 3.46 [95% CI: (0.69, 17.44)] within months 30-36 posttransplant. Only patients under 25 years had a notably increased risk beyond the first 2 posttransplant years. The risk of lymphoma differed by race, with Caucasian patients at nearly double the risk of African-Americans. Gender was not associated with lymphoma incidence. Conclusions. We found and quantified a time-varying relationship between renal transplant and lymphoma risk. This information can be used in combination with knowledge of established risk factors to guide the schedule of posttransplant monitoring.