Background: Agitation is a common feature of bipolar disorder and schizophrenia. Previous research indicates that specific symptoms impact caregiver burden in these conditions, but the impact of agitation on caregiver experience is poorly understood. The aim of this study was to characterise caregiver burden in providers of informal care for patients with bipolar disorder and schizophrenia who experience agitation.; Methods: In total, 297 matched patient and caregiver surveys were collected across the UK, Germany and Spain between October 2016 and January 2017. To be eligible, caregivers needed to provide informal care to a patient with a diagnosis of bipolar disorder or schizophrenia with agitation managed in a community setting and participating in the patient survey. The caregiver survey captured information on demographics and their role in managing the patient's agitation. Caregiver burden was assessed using the Involvement Evaluation Questionnaire. Descriptive analysis was conducted.; Results: Caregivers provided 38.3 h (SD ± 40.34) a week of support to the patient with 20% providing 50 h or more. Most caregivers reported that they recognised an episode of agitation all of the time (44%, n = 130) or sometimes (40%, n = 119). Verbal de-escalation techniques (talking (80%, n = 239) and soothing (73%, n = 218) were the most commonly reported strategies used by caregivers during an episode of agitation; 14% (n = 43) reported resorting to physically restraining the patient. Caregivers supervised rescue medication administration regularly (41%, n = 69) or occasionally (49%, n = 82). Mean Involvement Evaluation Questionnaire score was 32.2 (± 15.27), equivalent to 28.4 (± 13.56) in Germany, 35.6 (± 16.55) in Spain and 33.3 (± 15.15) in the UK. Involvement Evaluation Questionnaire scores were higher for caregivers who reported hostile (41.7 ± 17.07) lack of control (40.3 ± 16.35) and violent (39.5 ± 16.40) patient behaviours when agitated. Over excitement (31.8 ± 15.05), restless (32.6 ± 14.77) and tense (32.9 ± 15.64) behaviours were associated with a lower Involvement Evaluation Questionnaire score.; Conclusions: Caregivers are active participants in the recognition and management of agitation episodes. The substantial burden reported by these caregivers is impacted by factors including the number of hours of care provided, patient behaviours and country. These may be viable targets for effective interventions to reduce caregiver burden.