BACKGROUND Colophonium is a common contact allergen that is present not only in household products but also in occupational settings. OBJECTIVE To describe the sources of occupational exposure to colophonium and the occupations at risk of colophonium allergy. METHODS We reviewed patch test files from the years 2002 to 2017 at the Finnish Institute of Occupational Health for patients with allergic reactions to colophonium and abietic acid. We analysed the patch test, occupation and exposure data of 39 patients diagnosed with occupational allergic contact dermatitis (OACD) caused by colophonium. RESULTS Of the patients examined for suspected occupational dermatitis, 4.6% (n = 118) reacted positively to colophonium. The majority of the OACD patients worked in the wood industry, as machinists, or were involved in soldering or agriculture. The most common occupational sources of exposure were coniferous wood and wood-derived materials, followed by glues, metalworking fluids, and soldering materials. Colophonium is not always mentioned in safety data sheets (SDSs), and the sources of colophonium exposure are often materials for which there are no SDSs. CONCLUSIONS OACD caused by colophonium is quite common and occurs in a variety of occupations. SDSs provide poor information for exposure assessment. Patch testing with the patient's own materials was often useful in establishing the diagnosis.