The aim of this study was to evaluate the rejection rates of bulls in the behavioral assessment (libido and mounting capacity) and the importance of this step in the breeding soundness evaluation of 30,700 beef bulls in the state of Rio Grande do Sul, Brazil. Bulls from the following breeds were evaluated: Aberdeen Angus, Red Angus, Hereford, Polled Hereford, Devon, Shorthorn, Brangus, Braford, Montana, Santa Gertrudis, Charolais, Limousin, Brahman, Nelore, and Tabapua. In order to investigate the relationship between the binary variable (approved or rejected in different steps of the breeding soundness evaluation) and age groups (young and mature bulls), the Chi-Square test (PROC-FREQ) and the Tukey test were used. The general rejection rates in the breeding soundness evaluation were 13.7 and 22.7% for young and mature bulls, respectively. In the present study, problems in the sexual behavior of bulls accounted for the rejection of 3.6 to 5.2% of young and mature bulls, respectively. Lack of libido and/or mounting capacity were shown to be important problems in relation to the total number of possible causes of rejection of bulls in the breeding soundness evaluation. Several factors may affect the expression of libido and/or mounting capacity at pasture, and the conditions under which this step is carried out may influence the results. Performing behavioral assessment as part of the breeding soundness evaluation has been shown to be important to the thorough reproductive evaluation of bulls. The rejection of bulls in the behavioral assessment may suggest that this step should be performed regularly, rather than just being complementary to the standard breeding soundness evaluation.