Hallucinations are common in normal individuals and patients with schizophrenia and other psychotic disorders. Traditionally psycho-social approaches have emphasized the importance of environmental factors that contribute to variation of hallucinations. Using the Launay-Slade Hallucination Scale-Revised (LSHS-R), we investigated genetic and environmental influences on hallucinations in 598 pairs of healthy South Korean adolescent twins. Parameter estimates in the best-fitting model indicated that additive genetic and individual specific environmental factors for the LSHS-R were 33% (95% CI: 23-42%) and 67% (95% CI: 60-77%), respectively. There was no evidence for sex-specific genes for hallucinations. The magnitudes of genetic and environmental influences on hallucinations were similar in males and females. These results have implications in future molecular genetic studies that search for genes for hallucinations.