It is well established that individuals who engage in more positive social interactions report a broad array of benefit relative to those with fewer positive social interactions. Yet less is known about how, within individuals, naturally occurring social interactions in daily life relate to momentary indicators of health (e.g., mood, psychological, and physiological stress). The current study used ecological momentary assessment (EMA) to examine these within-person relationships, as well as complementary between-person relationships, among 115 adults (75% female; Mage = 41.21). Participants completed six EMA surveys per day for 3 days to report on whether they experienced any social interactions and whether the interactions were pleasant as well as on their mood, pain, tiredness, interest, and perceived stress; they also provided a salivary cortisol sample after each EMA survey. Multilevel modeling analyses showed that individuals felt more happiness and interest, and less sadness, tiredness, and pain, during moments when they were engaged in a social interaction versus when they were not. Individuals also reported less stress during more pleasant versus less pleasant social interactions. When examining between-person effects, we found evidence that people who gave more pleasant interactions generally reported more positive outcomes. This study presents evidence for intraindividual links between social interactions and momentary health indicators in daily life.