This study explores the attributions to which undergraduate university students ascribe academic achievement. Attribution theory was used as a means to understand scholastic success-failure. The questions that guided the study were the following: What are the causal attributions that predominate in students' academic achievement? Is there a difference between male and female students? Is there a difference if average grades and the number of failed subjects, factored as benchmarks of academic achievement, are considered? Do the measured attributions have any weight when predicting students' grades? A Likert scale measuring eight different attributions of academic achievement was applied to 165 students. The results showed that the most important attribution for academic achievement was intelligence. Sex-related differences were found in two attributes: calm and effort. In general, students with four failed subjects were those with the lowest averages measured in attributions. The variables that predicted good grades for male students were effort and good teachers, for female students, a liking for teachers, luck, and attention.