Individuals with autism spectrum disorders (ASD) commonly present with comorbid internalizing problems, including depression and anxiety. This elevated prevalence of internalizing disorders has been replicated in the literature for adolescents and adults with ASD, but the literature is less consistent in reporting prevalence statistics for young children with ASD. Results of this dissertation replicated the findings showing substantially elevated levels of internalizing symptomatology for participants ranging in age from 6 to 22 years using both parent- and self-report measures. Parents reported more internalizing symptoms than their children. Commonly used measures of affect and mood are flawed in ways that are particularly problematic for individuals with ASD; however, the Positive and Negative Affect Schedule (PANAS) and Positive and Negative Affect Scale for Children (PANAS-C) are formatted to avoid these problems. Rather than mimicking diagnostic criteria, items on these measures are simply lists of adjectives relating to positive (PA) and negative affective (NA) states. The original PANAS was created based on the Tripartite Model of Depression and Anxiety, in which depression and anxiety share low levels of NA, and can be differentiated by low PA in depression, but not in anxiety. In this model, PA and NA are considered two separate unipolar dimensions of affect. The primary aim of this dissertation was to describe the psychometric properties of the PANAS and PANAS-C, including evaluating the stability of the factor structure, reliability, and validity in an ASD population. Revisions to the measures were required to attain interpretable factor structures and acceptable internal consistency in this ASD sample, especially for the youngest participants (6 to 7 years) and convergent validity was fairly poor. Additionally, the structure of affect for these 6 to 7 year olds was revealed as bipolar, rather than unipolar. Overall, the PANAS-C is not recommended for use in young children, and requires further evaluation for older children, adolescents, and adults with ASD. Suggestions are made for items which could be eliminated, as well as for items that could be added to make the measure more appropriate for an ASD population.PhDPsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99865/1/buvinger_1.pd