The objective of this paper is to study the structure of temperament in mental retardates and its relationship with performance. A set of objective tests and a L-data scale were administered. Results indicated that a bidimensional structure was suitable for de L-data scale, showing two factors interpreted as extraversion and neuroticism. In T-data, a bidimensional structure was also found: velocity and quality. Relations between L-data and T-data suggest that velocity is a temperamental factor and quality is un ability factor.