Unbalanced sex ratio in rural areas is currently an endemic problem in most western countries that needs to be addressed if socially sustainable rural development is to be achieved. Higher percentages of females migrating from rural areas to the cities have given rise to an unequal spatial distribution of the sex ratio along the urban–rural gradient. In this paper it is proposed that temporal changes in rural–urban sex ratio differences in the young professional age group who are mostly independent and living outside the parental home should be included as a relevant factor in the framework of multi‐criteria monitoring of rural development policies. As a case in point, an analysis is carried out in continental Spain between 2000 and 2010 using the 30–39‐year‐old age group to focus on young people who for the most part have left the parental home. The overall results show that the sex ratio gap between rural and urban areas decreased during the decade in rural municipalities, independently of their size, which are contiguous to or at an intermediate distance from urban areas, as it did also in more remote medium‐sized and large rural municipalities. The gap did not vary significantly in the case of smaller and more remote rural municipalities, though there were specific regional tendencies upward or downward. The method can be applied to other study areas at different spatial and temporal scales.