OBJECTIVES: To investigate the medicine treatment cost of rheumatoid arthritis (RA) before and after treatment with biological drugs in the private health care sector of South Africa. METHODS: A quantitative retrospective drug utilisation review was performed on medicine claims data of a pharmacy benefit management company (PBM) in South Africa. Data for a four-year period (January 1, 2005 to December 31, 2008) were used to determine the medicine treatment cost of 141 RA patients before and after treatment with biological drugs (namely infliximab, adalimumab and etanercept). [RSA Rand (R)/$US = 6.38112 (2005); 6.78812 (2006); 7.06926 (2007) and 8.27505 (2008)].  RESULTS: Biological drugs represented 81.43% of the total medicine treatment cost of RA patients (n = R25,432,294.04). Other medication (excluding biological drugs) prescribed to RA patients before starting with biological items represented 8.86% (n = R2 254 330.44) of their total medicine treatment cost; those prescribed after treatment with biological drugs, represented 3.91% (n = R992,533.62). The number of prescriptions for other medication (excl. biological drugs), decreased from the period before to the period after treatment with biological drugs from 6271 to 2120. The average number of the other medicine items (excl. biological) per prescription decreased from 2.79 ± 2.30 before to 2.35 ± 1.86 after treatment with biological drugs. The average cost per biological drug (R8 073.61 ± 2 210.46) was practically significantly (d > 0.8) higher than the average cost of other medication prescribed before (R128.45 ± 155.93) and after (R198.66 ± 888.31) treatment with biological drugs. CONCLUSIONS: Although biological drugs used in the treatment of RA are very expensive, it seems that the number of other medication prescribed to RA patients, as well as the average number of items per prescription decreased after treatment therewith. Further research is needed to investigate future medicine treatment cost of RA patients treated with biological drugs.