The main aim of this thesis was to deepen our understanding of incidence, treatment, relative survival, mortality, and quality of life of patients with non-Hodgkin lymphoma (NHL) in a population-based setting. In chapter 1, a general introduction on NHL and the three different registries employed for the studies described in this thesis is given. In chapter 2, we studied incidence, treatment, relative survival, and mortality of patients with NHL. The incidence of indolent B-cell and T- and NK-cell neoplasms increased over time, whereas the incidence of aggressive B-cell neoplasms remained stable. The 5-year RS rates rose for indolent and aggressive mature B-cell neoplasms. The 5-year RS remained stable over time for T- and NK-cell neoplasms. In chapter 3, we focused on aggressive B-cell lymphoma, describing incidence, first-line treatment and survival. Incidence remained stable for DLBCL, while for MCL and BL the incidence increased for men and remained stable for women. Between 1989-1993 and 1994-1998, 5-year RS did not improve for patients with aggressive B-cell lymphoma. However, an improvement was observed from 1999-2004 to 2005-2010. This improvement was most prominent in patients aged <65 years. The main contributors to the improvement in survival in our study appear to be rituximab therapy, autologous stem cell transplantation, and use of more intensive chemotherapy. In Chapter 4, we focused on first-line treatment in patients with DLBCL. We demonstrated that R-CHOP14 and R-CHOP21 were equally effective. Besides, we demonstrated that R-CHOP14 were associated with significantly more polyneuropathy compared to R-CHOP21. Secondly, we demonstrated that 6x and 8x R-CHOP were as well equally effective modalities. Next, we compared 6x R-CHOP21 (± two additional cycles of rituximab; ±2R) to 6x R-CHOP14 (±2R), 8x R-CHOP14 and 8x R-CHOP21 among patients aged 18-64 years. OS was similar across the four regimens. Therefore, 6xR-CHOP21 could be considered as first-line regimen. In chapter 5, we analysed the ...