Close relationships are integral to who we are; they influence our sense of self (Berscheid, 1994), emotional well-being (Deci et al., 2006), and physical health (Cohen, 2004). However, close relationships are not immune to external stressors. One stressor that has been understudied with respect to close relationships is sleep loss (Troxel et al., 2007). Sleep loss is common in the general population (National Sleep Foundation, 2008), and pervasive in that it leads to psychomotor, affective, and cognitive deficits (Pilcher & Huffcutt, 1996). The present research investigated whether sleep loss hindered individual and interpersonal functioning. Participants were healthy undergraduate students who were in established romantic relationships of one year or longer. Sleep loss was experimentally manipulated such that participants experienced either a full night of sleep in their own homes or sleep deprivation in the laboratory. Affective, cognitive, and relationship measures were administered before and after the sleep manipulation. As expected, total sleep deprivation led to increased sleepiness and negative mood, as well as decreased self-reported sociability. In addition, sleep condition emerged as a significant moderator of closeness and interdependence when considering gender, relationship length, and attachment. These findings indicate that sleep loss does have a negative impact on close relationships, and this research is an important step in evaluating the proposed theoretical model.