Restricted interests are an established diagnostic symptom of autism spectrum disorder. While there is considerable evidence that these interests have maladaptive consequences, they also provide a range of benefits. This article introduces a new instrument, the Survey of Favorite Interests and Activities, and uses it to examine the nature of restricted interests in autism spectrum disorder. Respondents report substantial benefits of restricted interests as well as areas of difficulty. The Survey of Favorite Interests and Activities assesses Social Flexibility, Perseveration, Respondent Discomfort, Adaptive Coping, and Atypicality. All scales have Cronbach's a > 0.70. Age and socioeconomic status have little effect on Survey of Favorite Interests and Activities scales; nor does gender with the exception of interest Atypicality. The expected pattern of correlations with existing scales was found. Research and clinical implications are discussed.