Opioid use disorders are chronic and relapse is common. Both negative affect and craving have been suggested antecedents of relapse and have been shown to demonstrate within- and between-person variability, as well as association with each other. The present study extends previous research by examining the covariation of negative affect and craving both within-day and at the person-level during 12 days of treatment among opioid-dependent patients. Ecological momentary assessment (EMA) data were collected from 73 participants starting between 10 and 14 days after admission to an inpatient treatment facility. These data were analyzed using multivariate multilevel models and time-varying effect models. Results demonstrated strong association between negative affect and craving. Within-day, negative affect and craving were most associated in the early afternoon. At the person-level, association between negative affect and craving declined during the first week of data collection. Following this initial decline in association, negative affect and craving increasingly covaried during days 8-12 of data collection. To our knowledge, this is the first study to report a lagged increase in the association between negative affect and craving among patients during inpatient treatment for opioid dependence. Implications for research and treatment providers are discussed.Copyright © 2020 Elsevier Ltd. All rights reserved.