Description: This article discusses development of interests in children with autism. Abstract: By definition, children with autism have limited interests. While considerable efforts have been directed toward the social and communication difficulties faced by children with autism, less attention has been directed towards understanding the development and acquisition of new interests. Such understanding may help autism interventionists-establish increasingly diverse and complex interests thereby increasing reinforcing events, learning opportunities, activity participation, and social engagement. This paper describes an observational system for monitoring reinforcer diversity and event engagement during naturalistic teaching portions of an early intervention program. Data are presented for two children. It is suggested that such measures are necessary for two reasons. First, given the lack of empirical support and the importance of reinforcers, there is a need for measurement systems to monitor the development of interests in early intervention programs for children with autism. Second, there is a paucity of research addressing expansion of interests. Developing measurement systems increases the likelihood that evidence-based practices will emerge. Hopefully, these efforts will increase our knowledge, increase child preference for instruction, and open avenues for enhanced instructional and life opportunities based on expanded interests.