The aim of the present study was to compare body fat percent (BF %) using single-site near-IR reactance (NIR) and dual-energy X-ray absorptiometry (DXA) in a cohort of normal-weight (BMI < 25 kg/m2) black (n 102) and white (n 71); and obese (BMI ≥ 30 kg/m2) black (n 117) and white (n 41) South African women (18–45 years). NIR-derived BF % was significantly correlated with DXA-derived BF % in all groups: normal-weight black (r 0·55, 95 % CI: 0·40, 0·67, P < 0·001) and white (r 0·69, 95 % CI: 0·53, 0·79, P < 0·001) women; obese black (r 0·59, 95 % CI: 0·46, 0·70, P < 0·001) and white (r 0·56, 95 % CI: 0·30, 0·74, P < 0·001) women. NIR under-predicted BF% compared to DXA in black women (normal-weight, − 4·36 (sd 4·13) % and obese, − 3·41 (sd 3·72) %), while smaller mean differences were observed in white women (normal-weight, − 0·29 (sd 4·19) % and obese, − 0·81 (sd 3·09) %), irrespective of normal-weight or obese status (P < 0·001). In obese subjects, NIR-derived BF % did not measure values greater than approximately 45 %, while the maximum DXA-derived measure was 58 %. In conclusion, although there was a significant relationship between NIR- and DXA-derived BF %, NIR under-predicted BF % in normal-weight and obese black South African women compared to DXA, but to a greater extent in subjects with very high levels of adiposity (>45 %). The results of single-site NIR as a measure of BF % should therefore be interpreted with caution, particularly in women of African descent and in those with very high levels of adiposity.