Background: Race is commonly described in epidemiological surveys based on phenotypic characteristics. Training of interviewers to identify race is time-consuming and self identification of race might be difficult to interpret. The aim of this study was to determine the agreement between race definition based on the number of ascendants with black skin colour, with the self-assessment and observer's assessment of the skin colour. Methods: In a cross-sectional study of 50 women aged 14 years or older, from an outpatient clinic of an University affiliated hospital, race was assessed through observation and the self-assignment of the colour of skin and by the number of black ascendants including parents and grandparents. Reliability was measured through Kappa coefficient. Results: Agreement beyond chance between self-assigned and observed skin colour was excellent for white (0.75 95% CI 0.72–0.78) and black women (0.89 95% CI 0.71–0.79), but only good for participants with mixed colour (0.61 95% CI 0.58–0.64), resulting in a global kappa of 0.75 (95% CI 0.71–0.79). However, only a good agreement for mixed women was obtained. The presence of 3 or more black ascendants was highly associated with observed and self-assessed black skin colour. Most women self-assigned or observed as white had no black ascendants. Conclusions: The assessment of race based on the race of ascendants showed reasonable agreement with the ascertainment done by trained interviewers and with the self-report of race. This method may be considered for evaluation of race in epidemiological surveys, since it is less time-consuming than the evaluation by interviewers.