Research suggests strong associations between habitual sleep parameters (eg, mean duration, timing, efficiency), perceived stress, and insomnia symptoms. The associations between intraindividual variability (IIV; night-to-night within-person variation) in sleep, perceived stress, and insomnia have not been explored. This study examined associations between IIV in subjectively and objectively determined sleep parameters and to perceived stress in young adults with and without insomnia.Prospective longitudinal.Participants were 149 college students (mean age = 20.2 [SD = 2.4], 59% female) either with insomnia (n = 81; 54%) or without insomnia (n = 68; 46%).Participants completed 1 week of daily sleep diaries and actigraphy (to assess total sleep time [TST], sleep efficiency [SE], and circadian midpoint [CM]), the Perceived Stress Scale, and a diagnostic interview for determination of insomnia as part of a parent study.Greater IIV in actigraphy-determined TST (but not SE or CM) was independently associated with greater perceived stress, regardless of insomnia status. Greater IIV in sleep diary-determined TST, SE, or CM was not associated with perceived stress. Insomnia status was the most robust predictor of elevated perceived stress. There was a significant interaction between IIV in sleep diary-determined TST and insomnia status on perceived stress: Only in those without insomnia was greater IIV in sleep diary-determined TST associated with higher perceived stress.Maintaining a more consistent sleep duration may be associated with lower stress in college students. Future research is needed to clarify the directionality and implications of this association for treatment.