OBJECTIVES: This study sought to investigate the psychometric properties of two commonly used measures of social support in obesity, namely, the Social Support for Eating Habits (SSEH) and Social Support for Physical Activity (SSPA) scales. DESIGN: Cross-sectional and longitudinal study design. METHODS: Participants were 200 adults with obesity taking part in a 12-month cognitive behavioural weight loss programme. At pre-treatment, participants completed the SSEH and SSPA as well as measures of social support, motivation, self-efficacy, and health-related quality of life to assess concurrent validity. Predictive validity was assessed in terms of baseline SSEH and SSPA scores predicting post-treatment weight while controlling for pre-treatment weight. RESULTS: Factor analysis supported a two-factor solution for both the SSEH ('Encouragement' and 'Discouragement') and SSPA ('Participation' and 'Punishment') scales, with each subscale demonstrating acceptable internal consistency. While the results provided some support for the concurrent validity of the SSEH Discouragement and SSPA Participation subscales, there was mixed support for the SSEH Encouragement subscale and poor support for the SSPA Punishment subscale. No support was found in terms of predictive validity. CONCLUSIONS: The findings question the validity of the SSEH and SSPA scales in obesity, with behaviours deemed to be supportive in non-obese populations not necessarily perceived as such by people with obesity. The development of a psychometrically sound measure of social support in the obesity context is needed. Statement of contribution What is already known on this subject? Social support is a robust predictor of positive health outcomes. There is mixed support for the association between social support and weight-related outcomes in obesity. Discrepant findings may be due to social support measures of questionable reliability and validity in obesity. What does this study add? The SSEH and SSPA scales have questionable validity in obesity. Behaviours deemed to be supportive by family and friends may not be perceived as such by individuals with obesity. A psychometrically sound measure of social support in the obesity context is needed.