Patients having co-occurring borderline personality disorder and alcohol use disorders represent a common, but particularly severe and refractory subgroup. An individual, time-limited treatment, dynamic deconstructive psychotherapy (DDP), has been shown to be effective for this subgroup, but long-term outcomes are not known. Participants were recruited from a sample of 30 patients enrolled in a 12-month randomized controlled trial of DDP versus optimized community care (OCC). Outcomes were assessed after an additional 18 months of naturalistic follow-up. DDP participants received an equivalent amount of individual treatment and less group therapy than those receiving OCC, but demonstrated large, sustained treatment effects over a broad range of outcomes and achieved significantly greater improvement in core BPD symptoms, depression, parasuicide, and recreational drug use over the 30-month study. These results suggest that DDP is a cost-effective treatment that can lead to broad and sustained improvement for the dually diagnosed subgroup.