OBJECTIVES: To study the economic impact of a delay of treatment with 6 monts in couples with unexplained subfertility. METHODS: The economic analysis was performed from the perspective of the health care institution. Subfertile couples with unexplained subfertility and a moderate prognosis for treatment-independent pregnancy were randomly assigned to intra uterine insemination with controlled ovarian hyperstimulation (IUI COH) (early treatment group) or 6 months expected management (expectant management group). After the initial study of 6 months, couples were managed according to local protocol. We registered the number of treatment cycles with IUI and IVF, as well as the ongoing pregnancy rates in both groups. RESULTS: In the early treatment group, 94 couples started with IUI-COH and underwent 505 treatment cycles (5.4 cycle per couple). In the expectant management group, 67 couples started with IUI-COH and underwent 311 treatment cycles (5.4 cycle per couple). For IVF, In the early treatment group, 40 couples started with IVF and underwent 79 treatment cycles (2.0 cycle per couple). In the expectant management group, 27 couples started with IVF and underwent 53 treatment cycles (2.0 cycle per couple). Early treatment with IUI significantly increased the risk of a couples starting with IVF (RR 1.6, 95% CI 1.0 to 2.3). The average costs per couple were €3821 after early treatment versus €2322 after expectant management (P-value <0.001). When this saving in health care costs would be made available to the couples without an ongoing pregnancy after three years, these couples could undergo an additional three cycles of IVF per couple. CONCLUSIONS: Couples with unexplained subfertility and an intermediate prognosis for treatment independent pregnancy, delay of treatment for 6 months will result in reduction of health care costs of 1500 euros per couple without compromising the ongoing pregnancy rates.