Abstract Background: Little is known about the association between COPD and diabetes control parameters. Aims: To explore the association between comorbid COPD and longitudinal glycaemic control (HbA_1C) and systolic blood pressure (SBP) in a primary care cohort of diabetes patients. Methods: This is a prospective cohort study of type 2 diabetes patients in the Netherlands. In a mixed model analysis, we tested differences in the 5-year longitudinal development of HbA_1C and SBP according to COPD comorbidity (present/absent). We corrected for relevant covariates. In subgroup effect analyses, we tested whether potential differences between diabetes patients with/without COPD were modified by age, sex, socio-economic status (SES) and body mass index (BMI). Results: We analysed 610 diabetes patients. A total of 63 patients (10.3%) had comorbid COPD. The presence of COPD was not significantly associated with the longitudinal development of HbA_1C (P=0.54) or SBP (P=0.33), but subgroup effect analyses showed significant effect modification by SES (P<0.01) and BMI (P=0.03) on SBP. Diabetes patients without COPD had a flat SBP trend over time, with higher values in patients with a high BMI. For diabetes patients with COPD, SBP gradually increased over time in the middle- and high-SES groups, and it decreased over time in those in the low-SES group. Conclusions: The longitudinal development of HbA_1C was not significantly associated with comorbid COPD in diabetes patients. The course of SBP in diabetes patients with COPD is significantly associated with SES (not BMI) in contrast to those without COPD. Comorbid COPD was associated with longitudinal diabetes control parameters, but it has complex interactions with other patient characteristics. Further research is needed.