Objective: Little is known about the role of the mechanisms of accountability and performance optimization in clinical reasoning (CR) that guide the choice of homecare interventions. This study investigated the impact of these mechanisms on homecare occupational therapists’ (OTs) CR. Methods: An institutional ethnography (EI) approach was used with ten OTs participating in three homecare programmes in Québec. Observations (n = 41 days) and semi-structured interviews, informal interviews (n = 206) and formal interviews (n = 10), were carried out with these OTs. Twelve secondary key informants (colleagues, managers) were also encountered (n = 22 interviews) and administrative documents (n = 50) were collected. Data were analysed using the IE process. Results: Occupational therapists’ CR includes a constant concern with productivity, thereby modulating their assessments and interventions with patients. More specifically, OTs limit the time spent with each patient and the number of follow-ups. Their assessments and, consequently, their interventions, are often limited to the reason for referral, usually autonomy in personal care unless patient safety is threatened. Due to their requirement to categorize activities, accountability and optimization also generate a cognitive burden for OTs. The work measure used becomes a gold standard for OTs to assess the legitimacy of their activities and generates deviant behaviour in order to meet performance goals. Conclusions: The restricted range of OT interventions is incompatible with their holistic and patient-centred profession. Accountability and optimization may compromise the quality of their services, the scope of services offered, including prevention and health promotion activities, and, consequently, the achievement of the healthcare system objectives.