Positive valence systems are disrupted in late-life depression and in individuals at risk for suicide. The reward positivity (RewP) is an event-related potential measure of positive valence system function that relates to depression and anhedonia in children and young adults. However, it is unclear whether a reliable RewP signal can be elicited in middle-aged and older adults at high risk for suicide and, if so, whether this signal is similarly associated with clinical symptoms. In the current study, a RewP was elicited with a standard gambling task in middle-aged and older adults (N = 31) at discharge from a hospitalization for suicidal thought or behaviors. The resulting electrocortical response differed significantly for monetary wins compared to losses. Internal reliability of the RewP and the feedback negativity (FN) to monetary loss was good to excellent. Internal reliability of difference measures was lower but still largely acceptable, with residualized differences scores demonstrating stronger reliability than subtraction-based scores. A smaller residualized RewP, after accounting for the influence of the FN, was associated with greater severity of lassitude, an index of appetitive anhedonia. These findings set the groundwork for future studies of positive valence system function and depression in middle-aged and older adults at high risk for suicide.