Follicular lymphomas, as a prototype of all indolent lymphomas, are exquisitely radiation sensitive. This review paper highlights the clinical presentation of this lymphoma entity. Literature data are presented on first line curative irradiation in stage I and II patients, low-dose total body irradiation (TBI) in stage III and IV patients in first line and low-dose IF-RT (involved field radiotherapy) in patients with relapse. The clinical aspects of 2×2 Gy IF-RT in follicular lymphoma (FL) are presented as well as the in vivo imaging of the apoptotic cell death underlying the clinical response. Finally, by gene expression profiling, possible molecular-biological pathways are described involved in the low dose irradiation of FL.