BackgroundIt is important that easy-to-use measures like subjective questions about physical activity (PA) and sedentary behaviour are valid and reliable providing accurate measures, when they are used in health promotion work aiming to support people to improve their lifestyle habits such as PA. The aim of this study was to evaluate the concurrent validity of a structured interview form estimating self-reported PA and a question about sitting time used in Swedish targeted health dialogues in the context of primary health care.MethodThe study was conducted in the southern part of Sweden. To evaluate concurrent validity of the interview form, time spent in moderate-to-vigorous physical activities (MVPA) and energy expenditure related to MVPA estimated by an interview form was compared with the same measures assessed by an ActiGraph GT3X-BT accelerometer. To evaluate a question about sitting time, the Swedish School of Sport and Health Sciences’ single-item question about sitting time (SED-GIH) was compared with measures from an activPAL inclinometer. Statistical analyses included deriving Bland‒Altman plots and calculating Spearman’s rank correlation coefficients.ResultBland‒Altman plots indicated lower absolute variation in the difference between self-reported and device-based PA measures for lower PA levels, both for energy expenditure and time spent in MVPA. No systematic over- or underestimation was observed. The Spearman’s correlation coefficient between self-reported and device-based PA measures was 0.27 (p = 0.014) for time spent in MVPA and 0.26 (p = 0.022) for energy expenditure. The correlation coefficient between the single item question and device-based sitting time measures was 0.31 (p = 0.002). Sitting time was underestimated by 74% of the participants.ConclusionThe PA interview form and the SED-GIH question on sitting time may be of value in targeted health dialogues in primary health care with the intention to support sedentary and insufficiently physically active persons in increasing their physical activity and limiting their sitting time. The questionnaires are easy to use and are more cost effective than device-based measures, especially regarding population-based interventions conducted in primary health care for thousands of participants such as targeted health dialogues.Clinical trial registrationNot applicable.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13102-023-00690-8.