Objective. The Patient Activation Measure (PAM) is a 22-item measure that assesses patient knowledge, skill, and confidence for self-management. The measure was developed using Rasch analyses and is an interval level, unidimensional, Guttman-like measure. The current analysis is aimed at reducing the number of items in the measure while maintaining adequate precision. Study Methods. We relied on an iterative use of Rasch analysis to identify items that could be eliminated without loss of significant precision and reliability. With each item deletion, the item scale locations were recalibrated and the person reliability evaluated to check if and how much of a decline in precision of measurement resulted from the deletion of the item. Data Sources. The data used in the analysis were the same data used in the development of the original 22-item measure. These data were collected in 2003 via a telephone survey of 1,515 randomly selected adults. Principal Findings. The analysis yielded a 13-item measure that has psychometric properties similar to the original 22-item version. The scores for the 13-item measure range in value from 38.6 to 53.0 (on a theoretical 0-100 point scale). The range of values is essentially unchanged from the original 22-item version. Subgroup analysis suggests that there is a slight loss of precision with some subgroups. Conclusions. The results of the analysis indicate that the shortened 13-item version is both reliable and valid.Key Words. Patient activation, self-management, consumer roles in health care A previous publication described the development and testing of the Patient Activation Measure (PAM), which assesses patient self-reported knowledge, skill, and confidence for self-management of one's health or chronic condition (Hibbard et al. 2004). The 22-item PAM was developed using Rasch psychometric methods and is an interval level, unidimensional, Guttman-like measure. This current analysis is aimed at reducing the number of items in the measure without significant loss of precision. The methodology used to create the short form (PAM-13) is described and the psychometric properties of the short-form PAM are compared with those of the original 22-item PAM. Finally, the potential clinical and research applications of the short form measure are discussed.