This study quantified the tracking of physical activity from childhood to adulthood and described the nature of childhood physical activity experiences with respect to adult physical activity attitudes and behaviors. To address the first purpose 70 males (40 yrs) and 43 females (35-39 yrs) took part in a follow up study of the longitudinal Saskatchewan Growth and Development Study. Physical activity was measured from self-report questionnaires and correlation and percentile analyses conducted. There were no significant Spearman correlation coefficients in the male or female data. However, 44.3% of the males and 37.2% of the females remained in the same physical activity classification during childhood and adulthood. For the second purpose, 31 one-on-one, semi-structured, in-depth interviews were conducted. In the thematic analysis of the males'' data "significant others", "size and maturation", and "perception of ability" were prevalent. In the females'' data "transitions", "body image concerns", and "significant others" emerged. Thus, relationships, circumstances and perceptions from childhood influenced adult physical activity.