OBJECTIVES: WAVE-bd (Wide AmbispectiVE study of the clinical management and burden of bipolar disorder [BD]) is ongoing to address limitations of longitudinal BD studies to-date, few of which investigate caregiver burden. Objectives are to provide reliable, real-world data, including assessment of burden among caregivers (usually unpaid relatives or friends), an important consideration in BD patient management. METHODS: Multinational, multicentre, non-interventional, longitudinal study of patients diagnosed with BD with ≥1 mood event in the preceding 12 months (retrospective data collection from index mood event to enrollment, followed by a minimum 9 months’ prospective follow-up). Patient selection provided a representative sample of BD populations in daily practice. Caregiver burden was assessed using the Burden Assessment Scale (BAS), where scores range 19–76, with higher scores indicating greater burden. Assessment was carried out once during any part of the prospective follow-up for one caregiver only per patient. RESULTS: To-date, 583/2880 patients (BD-I: 21.8%; BD-II: 16.8%) have attended their baseline appointment with their primary caregiver (caregiver mean age 50.2 years; 57% female). The majority of caregivers were patients’ partners or parents (44.1% and 33.5%, respectively), with >10 years of education. The professional status of caregivers was: employed (47.4%), retired (22.7%), homemaker (16.6%), unemployed (5.8%) and other (7.4%). BAS scores were collected from 574 caregivers, and total caregiver burden was 47.6 ± 13.7 (n=424) for BD-I and 42.4 ± 12.6 (n=150) for BD-II (p=0.0003). Burden was recorded among caregivers of patients with (at inclusion) euthymia (43.8 ± 13.1; n=329), mania (47.7 ± 13.6; n=41), hypomania (51.6 ± 12.7; n=44), depression (49.9 ± 14.4; n=137), or mixed disease status (50.2 ± 9.5; n=20). CONCLUSIONS: This ongoing study provides multinational perspectives on the high burden experienced by caregivers of individuals with BD-I and BD-II in everyday clinical practice settings. Study funded by AstraZeneca; Clinical Trials Registry: NCT01062607.