Recognizing the demographic significance of the woman's age at first marriage or union and age at birth of the first child in the establishment of fertility levels, the information derived from the Encuesta Nacional de Salud Materno-Infantil 1987 was utilized to analyze both variables. Median age was analyzed by ethnic group, residence, education, marital status, and characteristics related to the work force. In all of these aspects, consistent differences were found. In additional, life tables were calculated for both events, applying the Coale model and utilizing the program NUPITAL. This model was very appropriate, given the goodness of fit, which was met for both legally married and consensually mated women. The model adequately describes the behavior of the Ladino and Indian populations separately, thus indicating the generalizeability of the model. Finally, demographic impact on the level of fertility of both age groups was determined and calculations made of the interbirth interval.