Flow is a state of optimal experience characterized by complete immersion in an enjoyable activity and has been associated with positive experience in activities. Self-expansion is a state of increase in the diversity and complexity of the self and has been linked with positive experience in relationships. Despite phenomenological similarities, the connection between these two states has not been examined. The current study used a correlational design to explore the degrees of overlap between these states by comparing them in general, situation-specific, and predictive contexts. It was expected that flow and self-expansion would occur at similar frequencies, be produced by similar situations, be positively correlated within given activities and relationships, similarly predict attraction to other within a given relationship, and be similarly predicted by a personality trait. Results indicated that these experiences do tend to co-occur. Among students reporting both experiences, the frequencies of the experiences were positively related, although flow experiences were reported as more frequent. Flow and self-expansion experiences were produced by similar sources across activities and relationships, and students tended to specify the same type of activity or relationship as the source of both experiences. As expected, flow and self-expansion were positively related within a given activity and within a given relationship. Both flow and self-expansion experienced in a relationship were positively related to attraction to the other, although the relationship between self-expansion and attraction was stronger than the relationship between flow and attraction. Neither flow nor self-expansion experienced in an activity was related to trait happiness, and there was no significant difference between these correlations. These results are reviewed in the context of previous research, and implications for theory, research, and practice are discussed. Finally, considerations for future research comparing these two theories, as well as other varieties of positive experience, are discussed.