OBJECTIVES: The aim of this study is to determine direct medical costs of treating patients with Chronic Lymphoid Leukemia (CLL) from the Brazilian Public Healthcare System perspective. METHODS: A retrospective longitudinal analysis of the Government administrative claims database (Datasus) was performed. Eligibility criteria were patients starting CLL (ICD-10 code C911) chemotherapy from Jan/2008 to Dec/2011, with complete information and no inconsistency in date of birth, gender. Outpatient and inpatient databases were combined through deterministic linkage. Outcome was direct medical costs (DMC), calculated as the sum of the medical claims for each patient included in the analysis, for a maximum period of 5 years or death or loss of follow-up, whichever comes first. DMC was categorized in chemotherapy, hospitalizations, and other outpatient costs.  RESULTS: From 5,100 patients with CLL identified in the database, 613 met eligibility criteria. Median follow-up time was 25 months. This population cohort had 54% males with average age at start of treatment of 66.4 ± 11.7 years. Patients received an average of 12.0 ± 9.4 months of chemotherapy treatment, with 71% of them treated by one type of chemotherapy regimen. Total DMC in this population was R$ 7,021,631.48 (average cost of R$ 6,404.52 ± 6,133.37 per patient-year), from which R$ 5,384,552.12 (77%) are related to chemotherapy, R$ 1,062,978.98 (15%) to hospitalizations and R$ 574,100.38 (8%) to other outpatient costs. Outpatient laboratory exams accounted for 6% (R$ 397,050.07) of total DMC. 30 (5%) patients underwent radiotherapy treatment, with total costs of R$ 53,944.96 (<1% of DMC).  A total of 862 hospitalizations were identified in 287 (46.8%) patients, with an average cost of R$ 1,233.15 ± 3,879.86 per hospitalization.  CONCLUSIONS: Patients with CLL represent a significant economic burden to the public health system. Chemotherapy and hospitalization costs accounts for more than 90% of the total costs.