The phenotypic, genetic, and environmental correlations between the Big Five factors of personality and loneliness were examined. At the phenotypic level, loneliness had a strong significant positive correlation with neuroticism, significant moderate negative correlations with agreeableness, conscientiousness, and extraversion, and a small positive correlation with openness. Both loneliness and personality were found to be heritable. Bivariate genetic analyses resulted in significant positive genetic correlations between loneliness and neuroticism and openness, and significant negative genetic correlations with agreeableness, conscientiousness, and extraversion. Significant unique environment correlations were found between loneliness and four of the five personality factors (all negative except neuroticism) and a non-significant correlation with openness. The results suggest common genetic and unique environmental factors play a role in personality and loneliness.