To develop a child- and adolescent-appropriate physical activity frequency questionnaire (PAFQ) in Tunisia, North Africa.

A PAFQ was developed from a physical activity (PA) inventory that comprised major activity components (at home, preparing meals, school time, transport, non-sport leisure, sports, prayer and sleeping time). Then, type and duration of each activity undertaken during the past week were estimated. Total energy expenditure (TEE) estimated by the PAFQ was compared with data derived from two criterion methods: heart-rate monitoring (HRM) and a 24 h PA recall (24h-R), both collected during a 3 d period including one weekday and two weekend days.

Two elementary schools and two high schools of the most developed and urbanized area, Greater Tunis.

One hundred and forty-two volunteer children and adolescents aged 10–19 years.

The PAFQ strongly was correlated with both HRM (r = 0·70; 95 % CI 0·62, 0·76) and 24h-R (r = 0·81; 95 % CI 0·77, 0·84). It featured acceptable agreement with both criterion measures, slightly underestimating TEE compared with 24h-R (−2·8 %, mean of individual differences −272·7 kJ/d; 95 % CI −490·6, −57·4 kJ/d) and moderately overestimating it compared with HRM (+11·3 %, mean of individual differences +1106·2 kJ/d; 95 % CI 845·8, 1366·6 kJ/d). Reliability ranged from moderate to good (weighted kappa coefficients from 0·47 to 0·78 and intra-class correlation coefficients between 0·79 and 0·86 for energy expenditure by PA categories), indicating strong agreement between the two assessments.

This PAFQ could be useful in the description and surveillance of PA patterns or for the evaluation of population-based interventions directed at promoting PA in Tunisian children and adolescents.