Introduction: The International Physical Activity Questionnaire (IPAQ) was developed to measure health-enhancing physical activity in adult populations. This study explores the concurrent validity of a modified version of the long IPAQ (the IPAQ-A) for the assessment of physical activity among adolescents. Participants and methods: In total, 248 healthy adolescents, divided into one older and one younger age group (aged 15-17 years (N 188) and 12-14 years (N 60), respectively) from nine Healthy Lifestyle by Nutrition in Adolescence (HELENA) Study centres across Europe, voluntarily participated in the study. Data on total physical activity, as well as activities in different intensities derived from the IPAQ-A, were compared using Spearman’s correlation coefficient and Bland-Altman analysis, with data from an accelerometer. Tertiles of total physical activity for the IPAQ-A and the accelerometer were compared using Kendall’s tau-b. Results: For the older age group, significant correlations between the instruments were found for time spent walking, for moderate and vigorous activities as well as for total physical activity (Rs 0.17-0.30, P < 0.05). No significant correlations were found for any of the variables studied in the younger age group. Kendall's tau-b showed low but significant correlations for tertiles of total physical activity (P < 0.001). Conclusions: The IPAQ-A has reasonable validity properties for assessing activities in different intensities and for total physical activity in healthy European adolescents aged 15-17 years. For adolescents aged 14 years and younger, the correlations were unsatisfactorily low and objective methodology, such as accelerometry, may be the appropriate alternative.