Dementia with Lewy bodies is a complex brain disorder and a key member of the Lewy body disease spectrum. Its genetic etiology is unclear, and information is scattered. However, the results of molecular genetic studies imply a genetic and mechanistic overlap with Alzheimer disease, Parkinson disease with dementia, and Parkinson disease. In this review, we provide a comprehensive overview of the current studies on dementia with Lewy bodies heritability, genetic etiology, and genetic heterogeneity. We conclude with a critical discussion of the missing heritability in dementia with Lewy bodies and encourage scientists to further explore the underlying mechanisms of this disease.