ArticleThe original publication is available at http://www.samj.org.zaObjective. To determine the molecular basis and establish a routine molecular diagnostic service for familial adenomatous polyposis coli (FAP) families in South Africa. Design. The coding region of the adenomatous polyposis coli (APC) gene in affected FAP kindreds was screened using heteroduplex analysis, single-strand conformation polymorphism analysis and the protein truncation test. Setting. Department of Human Genetics, University of Stellenbosch, and the Cancer Research Campaign Laboratories, Department of Pathology, University of Edinburgh and Molecular Medicine Centre, Western General Hospital, Edinburgh, Scotland (academic visit of 6 months). Subjects. FAP-affected individuals and at-risk family members in 28 apparently unrelated South African families. Results. A total of nine different APC mutations was identified, allowing DNA-based diagnosis in 20 families. Three of these mutations have not been described previously in other populations. Conclusion. Pre-symptomatic diagnosis using direct mutation detection is cost-effective and surgical intervention has the potential to prevent cancer in at-risk individuals from FAP families.Publisher’s versio