Background: The international literature has documented that self-determination is impacted by environmental factors, including living or work settings; and by intraindividual factors, including intelligence level, age, gender, social skills and adaptive behaviour. In addition, self-determination has been correlated with improved quality of life (QoL). This study sought to contribute to the growing literature base in this area by examining the relationship among and between personal characteristics, self-determination, social abilities and the environmental living situations of people with intellectual disabilities (ID). Methods: The study involved 141 people with ID residing in Italy. Healthcare professionals and social workers who had known participants for at least 1 year completed measures of self-determination, QoL and social skills. Analysis of variance was conducted to verify whether different levels of intellectual impairment were associated with different degrees of the dependent variables. The Pearson product-moment correlation was used to examine any relationships among dependent variables and IQ scores. Finally, discriminant function analysis was used to examine the degree to which IQ score, age, self-determination and social abilities predicted membership in groups that were formed based on living arrangement, and on QoL status (high vs. low). Results: The ANOVA determined, as expected, that participants with more severe ID showed the lowest levels of self-determination, QoL and social abilities. Discriminant function analysis showed that (a) individuals attending day centres were distinguished from those living in institutions in that they were younger and showed greater autonomy of choice and self-determination in their daily activities; (b) basic social skills and IQ score predicted membership in the high or low QoL groups; and (c) the IQ score predicted membership in the high or low self-determination groups. A MANOVA conducted to examine gender and age-level differences on self-determination found gender differences; women had higher self-determination scores than men. Conclusions: These findings contribute to an emerging knowledge base pertaining to the role of intraindividual and environmental factors in self-determination and QoL. In general, the study replicated findings pertaining to the relative contribution of intelligence to self-determination and QoL, added information about the potential contribution of social abilities, and pointed to the potentially important role of opportunities to make choices as a particularly important aspect of becoming more self-determined, at least in the context of residential settings.