If general practitioners are to provide effective genetic services, their knowledge and consultation skills need to improve. This study investigated whether oncogenetics training produces a lasting improvement in knowledge, consultation skills, satisfaction, and clinical applicability. Two training modules were developed: 1) E-learning module about hereditary breast, ovary, and intestinal cancer; 2) interactive group training on clinical skills (family history, oncogenetic risk assessment, referral possibilities) and attitude (medical ethical issues). A supportive Dutch 'GP and Genetics' website was also developed. Between September 2011 and April 2012, two controlled intervention trials were conducted, using patient simulations, checklists, and validated questionnaires. In total, 168 Dutch GPs evaluated the E-learning module (n = 80, 44 GPs completed all measurements) or the interactive group training (n = 88, 56 GPs completed all measurements). There was a significant and substantial improvement in oncogenetic knowledge (post-test 5.5%, p = 0.028; retention test 7.9%, p = 0.008; moderate effect sizes of 0.27 and 0.31, respectively) and in consultation skills (regression coefficient post-test 0.14, p = 0.005; regression coefficient retention test 0.11, p = 0.012; moderate effect sizes of 0.34 and 0.80, respectively). In summary, both training modules led to a sustained improvement in GPs' skills and competence in genetics. GPs were satisfied and positive about the practical applicability of the training. This training programme can serve as an example for future training activities with a view to improving genetic services.