ABSTRACTCaregivers of Amyotrophic Lateral Sclerosis (ALS) and Progressive Muscular Atrophy (PMA) patients often experience psychological distress. Yet, it is unclear which factors explain the variance in psychological distress. This study seeks to evaluate how care demands and perceived control over caregiving influence psychological distress using moderation and mediation analysis. Data were collected as part of a RCT and 148 partners of patients with ALS or PMA were included. Psychological distress was assessed using the Hospital Anxiety and Depression Scale. Care demands were operationalized as physical functioning (Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised) and behavioural changes of the patient (Amyotrophic Lateral Sclerosis-Frontotemporal Dementia-Questionnaire). Perceived control over caregiving was assessed using items adapted from the Job Content Questionnaire. Results showed that more behavioural changes and lower perceived control over caregiving were associated with higher levels of psychological distress in caregivers. Patients’ physical functioning was not significantly related to caregivers’ psychological distress. No moderation or mediation effects were found of perceived control over caregiving on the relationship between demand and psychological distress. Monitoring, psychoeducation and caregiver support with regard to behavioural changes in patients, seem to be important for the wellbeing of caregivers. Caregivers’ perceived control might be a target for future interventions.