In this paper, we explore the connection between education and wage inequality in Spain for the period 1994-2001. Drawing on quantile regression, we describe the conditional wage distribution of different populations groups. We find that higher education is associated with higher wage dispersion. A contribution of the paper is that we explicitly take into account the fact that workers who are and workers who are not in jobs commensurate with their qualifications have a different distribution of earnings. We differentiate between three different types of educational mismatch: "over-qualification", "incorrect qualification", and "strong mismatch". We find that while over-qualification and incorrect qualification are not associated with lower wages, strong mismatch carries a pay penalty that ranges from 13% to 27%. Thus, by driving a wedge between matched and mismatched workers, the incidence of strong mismatch contributes to enlarge wage differences within education groups. We find that over the recent years, the proportion of strongly mismatched workers rose markedly in Spain, contributing toward further within-groups dispersion.