The first ethnobotanical data on Pteronia divaricata is presented, which shows that the plant is an important traditional Cape medicine, especially in the Cederberg region (Western Cape Province) but also in the Middelpos and Nieuwoudtville districts of the Northern Cape Province. Surprisingly, not a single publication could be found that records any uses for the species. We accurately documented nine separate anecdotes, which include various medicinal uses (for the treatment of colds, fever, influenza, stomach pain, diarrhoea, back pain, chest ailments, high blood pressure and tuberculosis). The novel data also includes seven previously unrecorded vernacular names, namely flip-se-bos, inflammasiebos, pylbos, dassiebos, dassiepisbos, perdebos and boegabos. Since the species is poorly known, its general morphology, leaf anatomy and essential oil composition were studied. Oil is produced in secretory ducts along the midribs below the main vascular bundle; secretory trichomes are also present on the leaf surface. The oil is relatively complex and contains a combination of sabinene, myrcene, b-caryophyllene and bicyclogermacrene as main compounds with smaller amounts of limonene, p-cymene, tetradecane, pentadecane, terpinen-4-ol and δ-cadinene. Dichloromethane extracts exhibited antibacterial activity (especially against Bacillus cereus) at MIC values as low as 1.0 mg/ml. Other solvent extracts and the essential oils were less active.