['This secondary analysis evaluated the prevalence and stability of homelessness over one year among veterans entering substance abuse treatment and explored associations among housing status, treatment outcomes, and Veterans Affairs (VA) service utilization.', 'Participants in a trial of on-site primary care for veterans entering substance abuse treatment (N=622) were placed in four groups based on housing status: housed at baseline and final follow-up (41%), homeless at baseline and final follow-up (27%), housed at baseline but homeless at final follow-up (8%), and homeless at baseline but housed at final follow-up (24%). Groups were compared on treatment retention, changes in Addiction Severity Index (ASI) composite scores, and VA service utilization and costs.', 'Treatment retention and changes in ASI alcohol composites did not differ between groups. Compared with scores in the consistently housed group, the ASI drug composites improved less over time in the consistently homeless group (p=.031) and the ASI psychiatric composites improved less in the group housed at baseline and homeless at final follow-up (p=.019). All homeless groups were more likely than the consistently housed group to have inpatient admissions and incurred higher total treatment costs. The consistently homeless group was more likely to use emergency care than the consistently housed group.'] Do associations of housing status with substance abuse treatment and service use outcomes among veterans?