OBJECTIVE: To examine whether individual differences in Type D personality (combination of negative affectivity (NA) and social inhibition (SI)) could explain heterogeneity in perceived social support and relationship adjustment (intimate partner relationship) among people living with diabetes. DESIGN: In the Diabetes MILES-The Netherlands survey, 621 adults with type 1 or type 2 diabetes (54% female, age: 56 ± 14 years) completed measures of Type D personality (DS14), perceived social support and relationship adjustment. We used established DS14 cut-off scores to indicate Type D personality, high NA only, high SI only and reference groups. RESULTS: Participants from the Type D and NA only groups perceived lower levels of social support (Welch[3,259] = 37.27, p < 0.001), and relationship adjustment (Welch[3,191] = 14.74; p < 0.01) than those from the SI only and reference groups. Type D was associated with lower social support (lowest quartile; adjusted OR = 8.73; 95%CI = 5.05 ∼ 15.09; p < 0.001) and lower relationship adjustment (lowest quartile; adjusted OR = 3.70; 95%CI = 2.10 ∼ 6.53; p < 0.001). Type D was also associated with increased levels of loneliness. CONCLUSION: Participants with Type D and participants with high NA only tend to experience less social support and less relationship adjustment. Type D personality was also associated with more loneliness. Experiencing lower social support and relationship adjustment may complicate coping and self-management in people with diabetes.