The purpose of this study is to investigate the content-specificity of communication skills. It investigates the reliability and dimensionality of standardized patient (SP) ratings of communication skills in an Objective Structured Clinical Examination (OSCE) for final year medical students. An OSCE consisting of seven standardized patient (SP) encounters was administered to final-year medical students at four medical schools that are members of the California Consortium for the Assessment of Clinical Competence (N = 567). For each case, SPs rated students' communication skills on the same seven items. Internal consistency coefficients were calculated and a two-facet generalizability study was performed to investigate the reliability of the scores. An exploratory factor analysis was conducted to examine the dimensionality of the exam. Findings indicate that communication skills across the seven-case examination demonstrate a reliable generic component that supports relative decision making, but that a significant case-by-student interaction exists. The underlying structure further supports the case-specific nature of students' ability to communicate with patients. From these findings, it is evident that individual's communication skills vary systematically with specific cases. Implications include the need to consider the range of communication skill demands made across the OSCE to support generalization of findings, the need for instruction to provide feedback on communication skills in multiple contexts, and the need for research to further examine the student, patient, and presenting problem as sources of variation in communication skills.