BACKGROUND: Apathy is a common feature of Huntington’s disease (HD), even from early disease. However, patients are believed to lack insight into their own apathy and therefore clinicians and/or companions are relied upon to estimate the extent of a patient’s apathy. In addition, the evolution of apathy over time in HD has not been unequivocally established. OBJECTIVEs: The purpose of this study was to determine whether HD patient’s self-rated apathy scores were consistent with the scores given by companions who were also asked to rate the patients apathy. Furthermore, the clinical correlates of apathy and its stability over time were examined for both self-rated and companion-rated scores. METHODs: Apathy was measured in a large cross-sectional population of HD patients ranging from early to late stage disease (n = 106) using the Apathy Evaluation Scale; a subgroup of whom were followed longitudinally (n = 62) on average 18.7 (1.2 SD) months later. Comparisons were made between self-rated and companion-rated apathy and the relationship between apathy and motor, cognitive and functional performance was explored. RESULTS: Analysis of the cross-sectional data revealed that self-rated and companion-rated apathy were highly correlated, establishing the validity of using self-rated instead of, or in combination with, companion-rated assessments of apathy in future studies. Both self-rated and companion-rated scores had a relationship with motor and functional impairment, but had a complex relationship with cognition. The results of the longitudinal comparison revealed that apathy did not change over time in this cohort.CONCLUSIONs: Apathy can be equally well assessed by either patients or companions and does not change significantly over an18 month period. These findings have implications in the design of studies looking at treating this important aspect of HD.