Aim: The impact of maturity onset diabetes of the young (MODY) on quality of life (QoL) has never been examined. We assessed disease impact on QoL among patients with HNF1A-MODY and GCK mutation carrier status. Methods: The study included 80 patients with HNF1A-MODY and 89 GCK gene mutation carriers. We also examined 128 type 1 diabetes (T1DM) patients for comparison. Diabetes-specific QoL was assessed using the Audit of Diabetes Dependent Quality of Life questionnaire. Results: HNF1A-MODY and GCK-MODY groups had similar mean age (41.7 vs. 38.0 years, respectively) and BMI (24.1 vs. 24.3 kg/m2), whereas T1DM patients were on average younger (34.2 years) with similar BMI (25.0 kg/m2). Less than a third of GCK mutation carriers were on pharmacotherapy (n = 20, 31%), while the majority of HNF1A mutation carriers used oral drugs or insulin (n = 66, 82.5%). While current QoL was similar across the three groups (p = 0.66), two other major indices—the impact of diabetes on QoL and the average weighted impact (AWI)—differed among them (p < 0.001 for both comparisons). The impact of diabetes on patient QoL and AWI observed in both MODY groups was smaller than in T1DM. Etiological diagnosis of diabetes and a diagnosis of retinopathy were the only independent factors influencing the impact of diabetes on QoL and AWI in regression analysis. In HNF1A-MODY, all three major indices of QoL were more heavily influenced for patients on insulin in comparison to other treatment sub-groups. Conclusion: MODY has a smaller negative impact on QoL compared to T1DM. Mode of treatment further stratifies QoL decline for HNF1A-MODY subjects.