In some areas of the Red fox's range, such as northern Sweden, the number of yearling vixens which breed each year is dependent on food availability, and in years of poor food supply a high incidence of barren yearling vixens may occur. But most previous studies on Red fox reproduction record an overall low incidence of barren vixens, and it has therefore been assumed that most vixens breed in their first year. The present study shows that in suburban London, an area of high fox population density in which food availability is not limited, 52% of yearling vixens fail to breed. Possible reasons for this are discussed. It is also shown that senescence reduces the reproductive capability of vixens in their fifth and sixth breeding seasons.