Positive affect predicts improved glycemic control and longevity in adults with type 2 diabetes. We tested Developing Affective HeaLth to Improve Adherence (DAHLIA) a self-paced online intervention for type 2 diabetes that teaches positive affect skills such as savoring gratitude and acts of kindness. Participants (n = 49) were randomized to the fiveweek DAHLIA course or an emotion-reporting wait-list control. DAHLIA was understood and accepted by participants and showed good retention (78%). At post-intervention DAHLIA participants showed a significantly greater decrease in depression than controls (−4.3 vs. +0.6 points on the CES-D p = 0.05). Secondary analyses found that this effect was considerably stronger in intervention recipients recruited online than those recruited in person. Intervention recipients recruited online also showed significantly increased positive affect reduced negative affect and reduced perceived stress. There were no effects on measures of diabetes-specific efficacy or sense of burden or preliminary measures of health behaviors. This successful feasibility and efficacy trial provides support for a larger trial focusing more specifically on health behavior.