BACKGROUND: Rituximab (chimeric anti-CD20 monoclonal antibody) treatment is approved for chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL). Rituximab-abbs (first biosimilar approved in 2017) is expected to significantly reduce healthcare economic burden due to lower acquisition costs. This non-interventional, non-comparative study assessed real-world effectiveness and tolerability of rituximab-abbs and rituximab in treatment-naive patients with CLL or NHL. MATERIALS AND METHODS: Via an online physician survey, 46 UK-registered hematologists and oncologists retrospectively reported on randomly selected patients aged ≥18 years with CLL or NHL with rituximab-abbs or rituximab as first-line immunotherapy. Overall, 201 patient charts were examined across 4 cohorts: rituximab-abbs in CLL, rituximab-abbs in NHL, rituximab in CLL, rituximab in NHL. RESULTS: Demographic profiles across cohorts were similar. Most patients (94 %-100 %) received combination therapy (rituximab-abbs or rituximab mainly with chemotherapy). For both treatments, overall response rate (94 %-98 %) and 1-year overall survival (98 %-100 %) were very high for patients with CLL or NHL. Most common serious adverse events were neutropenia, fatigue, anemia and infusion reactions. The majority of patients (54 %-66 %) did not experience a grade ≥3 adverse event. Healthcare resource utilization was similarly high across cohorts, driven by diagnostic testing, oncologist office visits, and day-case hospital admissions; many patients required supportive medical therapies. Mean annual savings of ∼£1000/patient driven by acquisition costs occurred with rituximab-abbs versus rituximab, administration costs were similar. CONCLUSION: Rituximab-abbs and rituximab demonstrated similar effectiveness and tolerability in treating CLL and NHL in routine UK clinical practice and demonstrate the utility of the biosimilar as a cost-saving alternative treatment.