To identify generalizable ways that comorbidity affects older adults' experiences in a health service program directed toward an index condition and to develop a framework to assist clinicians in approaching comorbidity in the design, delivery, and evaluation of such interventions.A qualitative data content analysis of interview transcripts to identify themes related to comorbidity.An outpatient low-vision rehabilitation program for macular disease.In 2007/08, 98 individuals undergoing low-vision rehabilitation and their companions provided 624 semistructured interviews that elicited perceptions about barriers and facilitators of successful program participation.The interviews revealed five broad themes about comorbidity: (i) "good days, bad days," reflecting participants' fluctuating health status during the program because of concurrent medical problems; (ii) "communication barriers." which were sometimes due to participant impairments and sometimes situational; (iii) "overwhelmed," which encompassed pragmatic and emotional concerns of participants and caregivers; (iv) "delays," which referred to the tendency of comorbidities to delay progress in the program and to confer added inconvenience during lengthy appointments; and (v) value of companion involvement in overcoming some barriers imposed by comorbid conditions.This study provides a taxonomy and conceptual framework for understanding consequences of comorbidity in the experience of individuals receiving a health service. If confirmed in individuals receiving interventions for other index diseases, the framework suggests actionable items to improve care and facilitate research involving older adults.