Aims: Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive condition caused by deposition of transthyretin amyloid fibrils in the heart and is associated with poor quality of life and a shortened lifespan. This study aimed to describe the prevalence, clinical characteristics, and mortality of patients with ATTR-CM, using multiple national health registers in Denmark, Finland, Norway, and Sweden. Methods and results: Transthyretin amyloid cardiomyopathy patients were identified during 2008–2018 using a combination of diagnosis codes for amyloidosis and heart disease and were matched to patients with non-ATTR heart failure (HF). An identical study design was used in each country to facilitate comparison and aggregation of results. A total of 1930 ATTR-CM patients were identified from national health registers in the four countries. In 2018, prevalence of ATTR-CM per 100 000 inhabitants ranged from 1.4 in Denmark to 5.0 in Sweden; a steep increase over time was observed in Sweden and Norway. Median survival from diagnosis was 30 months for ATTR-CM patients and 67 months for matched HF patients. Survival was significantly lower for female than for male ATTR-CM patients (median survival: 22 and 36 months), while no significant difference was observed in the HF cohort. Conclusions: This study provides the first nationwide estimates of the prevalence, clinical characteristics, and mortality of patients with ATTR-CM, using identical study design across several countries. Findings corroborate previous case series showing high mortality in ATTR-CM, two-fold higher than for other HF patients and higher in women than men, highlighting the need for more precise and early diagnosis to reduce the disease burden.