OBJECTIVES: To estimate the treatment costs of rheumatoid arthritis, psoriasis, Crohn’s disease and ulcerative colitis in the Brazilian private health care system. METHODS: Treatment costs were gathered from a claims database with over four million beneficiaries for rheumatoid arthritis (AR), psoriasis (Pso), Crohn’s disease (CD) and ulcerative colitis (UC). Patients were identified according to CID10 codes and observed between June 2009 and August 2011. Treatment costs included hospitalization, drug, procedures, exams, equipment and other costs. RESULTS: In total 269 patients received treatment for AR, Pso, CD and UC in the Brazilian health care system, with an expenditure of about R$ 13 million. Over 78% of expenditure was due to drug spending, followed by hospitalization (8%), and materials (6%). Over R$ 8.2 million (63%) were spent with 116 CD and UC patients, resulting in an average cost of R$70.939,84 per patient. For 144 AR patients, expenditure totaled R$ 4.4 million (34% of the total spending) with an average cost per patient of R$30.834,06. Nine patients were identified with psoriasis, with a total spending of R$334.756 (2,57%), an average of R$ 37.195,11 per patient. On average, AR patients were hospitalized for 17 days with a total cost of R$181.422, followed by CD and UC patients hospitalized for 15 days on average with a total cost of R$ 965.507. Psoriasis patients were hospitalized on average for 4 days, with R$ 15.953 spend on average. CONCLUSIONS: Drug spending is the main driver behind health care spending in AR, Pso, Cd and UC in the Brazilian private health care system. Despite the lowest hospital stay, on average psoriasis patients spend more than RA patients in the hospital. Psoriasis represents the lowest share of total costs due to a low number of patients observed with this disease, indicating these patients might not have access to treatment.