OBJECTIVES: To highlight the importance in establishing age and gender bands with the aim of explaining the level of pharmaceutical expenditure of each Primary Health Care Team (PHCT). METHODS: Thanks to the advances of information systems and the introduction of the Personal Health Card, it has been possible to calculate the cost per inhabitant (according to age and gender) taking into account the expense generated through prescriptions produced by inhabitants assigned to the Public Health System (Central Register of Insured). RESULTS: According to some established criteria, 20 bands have been determined. It is proved that 10% of the population is concentrated in the 67 - 77 year old band and the expenditure that it generates is 33% of the total expense. However, the 9 - 12 year old and 33 - 39 year old bands together (15% of the population) only represent 3.8% of the total expense. Gender is also a relevant variable. Women have a higher level of expense than men for ages comprised between 21 and 72 and for those above 89 years old. There are alternations in the maximum values for gender in the 0 to 20 years old band. CONCLUSIONS: This study reflects the need to determine an optimum number of bands; that is, to add the information in some specific intervals that allow us to carry out an efficient analysis without losing the necessary perspective in order to obtain related conclusions with the aim of the study. It proves that a previous analysis is essential to evaluate the behaviour of the cost per inhabitant of a PHCT.