Peterson & Seligman’s model of character strengths and virtues is the basis for the ‘growing up strong’ scale used in this work. The objectives were to determine the psychometric properties, to compare these strengths according to sex and age, and to specify which of these predict psychological wellbeing. Instrumental, cross-sectional, descriptive and non-ex- perimental research involving 257 adolescents from Montevideo. The findings confirmed factorial and convergent validity of the scale and showed internal consistency values of 0.91. Women scored higher on curiosity (Z = 2.81, p<0.01), perspective (Z = 3.97, p<0.001), kindness (Z = 3.20, p<0.01), love (Z = 4.09, p<0.001) and equity (Z = 3.33, p<0.01), while men scored higher on enthusiasm (Z = 3.35, p<0.01) and leadership (Z = 2.38, p<0.05). Differences according to age were found in persistence (H = 8.80, p<0.05), teamwork (H = 9.51, p<0.05), prudence (H = 13.19, p<0.01) and self-regulation (H = 11.61, p<0.01). Strengths such as creativity (OR = 2.38, p<0.001), courage (OR = 2.05, p<0.001), kindness (OR = 3.48, p<0.001) and gratitude (OR = 2.83, p<0.001) predicted high scores of psychological well-being, correctly classifying 89.92% of the subjects. Similar results were found in the other dimensions of this construct. It is concluded: (a) the ‘growing up strong’ scale presents adequate psychometric properties that suggest its use to measure the construct in adolescents; (b) there are differences in some character strengths according to sex and age; and (c) the promotional role of character strengths in psychological well-being is verified.