This study analysed the live birth rates in 760 couples referred in 1994 to St Mary's Hospital, Manchester, a non-fee-paying National Health Service (NHS) centre, who had waited for up to 4 years for IVF treatment. These live birth rates were compared with those of 199 couples referred at a similar time to Manchester Fertility Services, a fee-paying unit, where they received IVF treatment shortly after referral. The waiting time was advantageous in that 17.8% (135 of 760) of the couples referred to St Mary's Hospital conceived without IVF treatment, 60% within one year of referral. However, the waiting time was detrimental to women aged 30-34 in whom treatment was delayed by 3-4 years. Only 26.8% (204 of 760) of couples originally referred eventually received NHS-funded IVF treatment at St Mary's. A waiting time not exceeding 18 months would allow most spontaneous conceptions and reduce the adverse effect of prolonged waiting on the take-up rate for treatment and on the chance of success in the older women.