Background: The Patient Activation Measure (PAM) is a recognized measure of how active patients are in their care, and has been translated into several languages and cultural contexts. Patient activity, self-care, and health literacy have become increasingly important aspects of health care, and thus reliable measures of these are needed. However, a Swedish translation of PAM is currently lacking. The aim of the study was to translate and assess the validity and reliability of the Swedish PAM-13. Methods: A self-report questionnaire was handed out to 521 patients at ten medical, geriatric, and surgical wards, and one Virtual Health Room. The Rasch model was employed, using the partial credit model, to assess the functioning of the PAM scale, item fit, targeting, unidimensionality, local independence, differential item functioning (DIF), and person-separation index. Evidence of substantive, content, structural, and external validity was examined. Results: Of the 521 patients who were consecutively handed a questionnaire, 248 consented to participate, yielding a response rate of 47.6%. The average measure for each category advanced monotonically. The difficulty of the PAM items ranged from - 1.55 to 1.26. The infit and outfit values for the individual items were acceptable. Items 1, 2, and 4 showed disordered thresholds. The mean person location was 1.48 (SD = 1.66). The person-item map revealed that there were no item representations at the top of the scale. The evidence for unidimensionality was ambiguous and response dependency was seen in some items. DIF was found for age. The person separation index was 0.85. Conclusion: The Swedish PAM-13 was reliable, but was not conclusively found to represent one underlying construct. It seems that the Swedish PAM-13 lacks strong evidence for substantive, content, and structural validity. Although valid and reliable measures of ability for activation in self-care among patients are highly warranted, we recommend further development of PAM-13 before application in everyday clinical care.