Abstract This longitudinal study evaluated the association between the incidence of youth overweight/obesity (Ow/Ob) and low levels of cardiorespiratory fitness (CRF) over 4 years and youths' and their parents' demographic and nutritional characteristics. The randomized sample comprised 398 youth, aged 7-17 years at baseline, from a city in southern Brazil. Subjects were classified as being Ow/Ob according to international body mass index (BMI) parameters. Parental weight and height were determined by direct questioning. Youth CRF was measured by a 9-minute walk-and-run test. The cumulative incidences of Ow/Ob and of low CRF levels were 25.1% and 20.5%, respectively. Relative to other youth, youth who were classified as "unhealthy" at baseline (with respect to CRF) and by the fourth year were more likely to be classified as Ow/Ob (relative risks: 1.12 and 1.10, respectively). Youth whose mothers were categorized as Ow/Ob were at higher risk of being classified as Ow/Ob than youth whose mothers had normal BMIs (relative risks: 1.19 at baseline and 1.20 in the fourth year). The incidence of Ow/Ob among the former youth was associated with low CRF levels and with maternal Ob.