BACKGROUND : The South African Children's Act No. 38 of 2005 requires paediatric medical consent from 12 years of age. OBJECTIVE : To determine children's ability to provide informed consent for medical treatment. METHODS : Assessment used hypothetical treatment storyboards and structured interviews for assessment of 100 children (aged 10 - 17 years), and 25 adult controls, using a standardised scoring tool to test understanding, ability to deliberate treatment choices, and provide rational reasons. Statistical analysis involved multivariate analyses of variance (MANOVAs) and analysis of variance (ANOVA). RESULTS : The female:male ratios for children and adults were 1:0.92 and 1:0.98, respectively. Children⩾12 years were competent with regard to treatment choices (p<0.001), while 10-year-olds could deliberate reasonable outcomes, similar to adults (p<0.001). However, only children 12 years and older could provide rational reasons, where abstract concepts were not involved, whereas children who were⩾14 years old were able to provide rational reasons involving abstract concepts. The actual understanding of choices, compared with adults, was only observed in children older than 14 years (p<0.001). Gender was not a statistically significant denominator. CONCLUSION : Children of 12 years and older are competent to make medical decisions, but the understanding of medical treatment choices under the age of 14 years is not clear.