The objective of this study is to determine overall response rate, event-free survival, time-to-progression, time-to-next-therapy, and freedom-from-relapse in patients with low-grade lymphoma in first or second relapse treated with Zevalin followed by 2 years of Rituxan maintenance therapy in a multicenter, community-based setting, as well as evaluate relative response rates in populations with and without prior rituximab therapy, in first versus second relapse, and with and without bulky (> 5 cm in greatest diameter) disease.