This observational study will monitor and register infusion-related adverse events and their handling in patients with chronic lymphocytic leukemia on treatment with MabThera (rituximab). Data will be collected from patients receiving intravenous MabThera at a dose of 375mg/m2 in cycle 1 and 500mg/m2 in subsequent cycles at each treatment visit for up to 6 months. Target sample size is 100 patients.

Inclusion Criteria:

• adult patients, >/= 18 years of age
• chronic lymphocytic leukemia treated with rituximab (MabThera)
• rituximab (MabThera) dosage 375 mg/m2 in cycle 1, 500 mg/m2 in subsequent cycles
• informed consent to data collection

Exclusion Criteria:

• participation in an interventional clinical study

CLL patients receiving standard of care rituximab infusions at haematological or medical clinics