Obstructive sleep apnea (OSA) is a serious disorder with significant daytime consequences. Treatment for OSA most commonly takes the form of positive airway pressure (PAP). Although effective, PAP adherence is often below expectations. Previous studies have suggested that early PAP use can predict long-term adherence, but these studies have not been replicated, nor has follow up been longer than 3 months. This article presents a replication study enhanced by a longer follow up and additional data to suggest that 6-month adherence can be predicted within the first days of PAP use. This article also discusses how this might relate to the experience of significant side effects of treatment.