Feeling certain about who one is and their place in the world is fundamental to human psychological functioning; however, significant life transitions, such as retirement, may prompt uncertainty about the self. This study introduces the concept of retirement self-uncertainty, or individual perceptions that the self-concept in retirement is unknown. In this study, we establish retirement self-uncertainty as a relevant psychological response for understanding the retirement adjustment process. We propose and test a conditional process model of retirement self-uncertainty using a time-lagged study of retired adults living in the United States. We find that the involuntariness of the retirement decision and financial hardship during retirement were positively associated with retirement self-uncertainty; subjective health status during retirement was negatively associated with retirement self-uncertainty. Calling orientation, or perceptions that pre-retirement work held significant meaning and purpose, strengthened the positive relationship between financial hardship and retirement self-uncertainty, but did not moderate relationships between involuntary retirement and subjective health with retirement self-uncertainty. Finally, retirement self-uncertainty was negatively associated with retirement satisfaction and psychological well-being. Our study expands insight into how uncertainty manifests during the retirement transition, offering new understanding of how and when uncertainty about the self-concept hinders adjustment.