Personality disorders, especially in older adults, are among the most difficult psychiatric disorders for nurses to assess. When aging further complicates these disorders, nurses' therapeutic skills are challenged. It has long been thought that personality disorders "age out," but new research indicates that personality disorders may in fact continue throughout the life span. In addition, the primary and secondary changes of aging further complicate assessment. Assessment of personality disorders in older adults may also be distorted by ageist stereotypes and a lack of understanding of cultural context. Likewise, nurses must be careful about misinterpreting "eccentric" older adult behavior as a personality disorder. In this article, we focus on assessment challenges in older adults to help nurses distinguish between characteristics of personality disorders, stereotypes, and eccentricities in this population.