BackgroundClinical learning takes place in complex socio-cultural environments that are workplaces for the staff and learning places for the students. In the clinical context, the students learn by active participation and in interaction with the rest of the community at the workplace. Clinical learning occurs outside the university, therefore is it important for both the university and the student that the student is given opportunities to evaluate the clinical placements with an instrument that allows evaluation from many perspectives. The instrument Clinical Learning Environment and Supervision (CLES) was originally developed for evaluation of nursing students’ clinical learning environment.The aim of this study was to adapt and validate the CLES instrument to measure medical students’ perceptions of their learning environment in primary health care.MethodsIn the adaptation process the face validity was tested by an expert panel of primary care physicians, who were also active clinical supervisors. The adapted CLES instrument with 25 items and six background questions was sent electronically to 1,256 medical students from one university. Answers from 394 students were eligible for inclusion. Exploratory factor analysis based on principal component methods followed by oblique rotation was used to confirm the adequate number of factors in the data.Construct validity was assessed by factor analysis. Confirmatory factor analysis was used to confirm the dimensions of CLES instrument.ResultsThe construct validity showed a clearly indicated four-factor model.The cumulative variance explanation was 0.65, and the overall Cronbach’s alpha was 0.95. All items loaded similarly with the dimensions in the non-adapted CLES except for one item that loaded to another dimension. The CLES instrument in its adapted form had high construct validity and high reliability and internal consistency.ConclusionCLES, in its adapted form, appears to be a valid instrument to evaluate medical students’ perceptions of their clinical learning environment in primary health care.Electronic supplementary materialThe online version of this article (doi:10.1186/s12909-016-0809-8) contains supplementary material, which is available to authorized users.