<h3>Background</h3> There are an important number of patients with osteoarthritis (OA) that are misdiagnosed as rheumatoid arthritis (RA) in general practice in Colombia. They are treated as such with disease modifying anti-rheumatic drugs (DMARDs), leading to higher economic costs for health system. <h3>Objectives</h3> The aim of this study was to calculate the possible direct economic costs of the care of OA patients misdiagnosed as RA in a 36 month period in a cohort of patients derived to a specialized RA center in Colombia. <h3>Methods</h3> A descriptive cross sectional study was performed. Patients derived during a 36 month period to a RA specialized center with presumptive diagnosis of this disease and found finally diagnosed with OA were included in analysis. We described the direct costs in colombian pesos (COP) of their care assuming an average of 4 visits/year to general practitioner (8.400 COP/consultation), 2 visits/year for physiatrist and orthopedics (33.995 COP/consultation) and 4 set/year of conventional laboratories (92.161 COP/set). Cost of medication doses were calculated for an average use of methotrexate, sulfasalazine, chloroquine and prednisolone (39.620 COP/monthly). Indirect costs were not calculated. <h3>Results</h3> We found 1108 OA patients misdiagnosed as RA in a period of 36 months. For each patient we calculated 33.600 COP/year for general practitioner visits, 135.980 COP/year for specialized medicine visits, 368.644 COP/year for laboratory sets and 475.440 COP/year for medications. This leads to a total cost of 1.011.504 COP/year per patient. From a total of 1108 misdiagnosed patients the cost rises to 1.103.195.712 COP/year. These patients had an average of 4.5 years of wrong treatment for their misdiagnosis, making the cost rise up to 5.054.128.704 COP (2.641.990 million US dollars). <h3>Conclusions</h3> There is an important economic implication of the misdiagnosis of OA as RA, being this the most frequent mistake in the diagnosis of this disease. The implementation of educational programs for health care primary physicians and specialized RA centers could save this amount of money for the health system in Colombia. <h3>Disclosure of Interest</h3> None declared