The purpose of this study was to determine some parental predictors of physical inactivity in Spanish adolescents. The sample comprised 1,978 children, aged between 12 and 16 years. A quantitative and qualitative technical triangulation was employed. The study analyzed data of the parents' educational level, the importance they grant to physical-sport activities, and their physical-sport practice. Quantitative technique: a questionnaire (MACOFYD) was used to collect the data. Descriptive, bivariate, and multinomial regression analyses were employed. Statistical significance was set at p < 0.05. Qualitative technique: four discussion groups were conducted, consisting of parents, physical education teachers, teachers of other subjects, and children aged between 12 and 16 years. The results indicated that adolescents are four times more likely to be physically inactive if their parents have never exercised (odds ratio [OR] = 4.065, and = 3.487, for the fathers and mothers, respectively, p < 0.05). When parents grant “some” or “much” importance to physical-sport practice, adolescents are less likely to be physically inactive (OR = 0.185 and 0.118 respectively, p < 0.01). No significant correlation was found between adolescents' physical-sport activity and parents' educational level. However, young people reproach their parents because they emphasize academic goals more than physical-sport practice-an observation that teachers also confirm. Young people perceive their parents as being the education agents with the greatest influence over their inactive lifestyles. Many parents are unaware of their influence and, therefore, do not take responsibility, declaring that the teachers' influence is greater.