The records of 19 cats treated for stage I nasal lymphoma with radiation therapy and chemotherapy were reviewed to determine response to therapy, treatment outcome and possible prognostic indicators. All cats were treated with megavoltage radiation therapy to a total dose ranging from 22 to 48 Gy (median dose = 42 Gy). All cats were prescribed at least 6 months of multiagent chemotherapy. The median progression-free interval for all cats was 945 days (31 months). Two cats did not achieve clinical remission. Of 17 cats evaluable for relapse, 10 (58.8%) were progression free during the entire follow-up period. Four cats (23.5%) suffered local recurrence, while three (17.6%) experienced distant relapse. The median survival time was 955 days (31.4 months). The only variable found to have a significant negative impact on survival was destruction of the cribriform plate before therapy (P= 0.002). The long progression free and survival times reported here indicate that cats with stage I nasal lymphoma treated with aggressive local and systemic therapy can have a favorable outcome when compared with other anatomic forms of lymphoma. Despite strong clinical responses to the multimodality therapy used, the fact that three (17.6%) cats relapsed distantly supports the recommendation that treatment with radiation therapy alone is insufficient until further prospective studies can be performed.