The following is a description of the findings of a longitudinal exploratory and descriptive research study of 22 persons nominated as expert self-managers of Type 1 diabetes. It entailed an initial interview about previous experiences with self-management, self-recorded taped diaries about self-management decisions for 1 week each, and face-to-face interviews following each weeklong recording of self-management decisions. The study generated a grounded theory about the development of expertise in diabetes self-management. The development of expertise was found to occur as transition through two or more phases, to be individualized, and to involve a complex interplay between social, contextual and personal factors, including the individual's developmental age. The research fIndings challenge the traditional understanding of rebellion in self-management as a manifestation of adolescence, behaviors other than active control as testimony to ineptitude in self-management, metabolic control as the indicator of self-management ability, and the role of others as collaborators in self-management.