Aim: To examine the relative cost-effectiveness of predictive genetic tests for familial breast and ovarian cancer provided by Genetic Services of Western Australia. Methods: The relative cost-effectiveness was assessed using a decision analytic model. Results: The cost and outcomes of genetic testing was compared in first-degree relatives of known BRCA1/2 mutation-carriers who have a 50% risk of carrying the mutated gene (intervention group) to individuals with the same a priori risk but who do not undergo a genetic test (control subjects). Since genetic testing enables the restriction of intensive surveillance to individuals with an identified BRCA1/2 gene mutation, net savings in the period observed (age 25-70) were $980-$1008 per woman in the ovarian intervention group and $1681-$1795 per woman in the breast intervention group, and delayed the onset of breast cancer (6mths BRCA1, 3mths BRCA2). Compared to control subjects undergoing population surveillance, it was estimated the onset of breast cancer could be delayed at a total net cost of $3055 (5.1yrs) to $3389 (3.2yrs) for women in the breast intervention group with BRCA1/2 mutations. Since population surveillance is not currently recommended for ovarian cancer, control subjects undergoing no surveillance were compared with the intervention group. The onset of ovarian cancer was delayed at a net cost of $1630 (3.5yrs) to $2509 (1.2years) for women with BRCA1/2 mutations. Conclusions: Testing allows targeted high-level surveillance for gene mutation carriers, which ensures the cost-effective use of resources and reduces cancer-related morbidity if clinical recommendations for intervention are adopted.