Abstract Background/Aim People with diabetes are at a greater risk of serious complications from Coronavirus disease (COVID-19). Self-management of diabetes is therefore of paramount importance. The purpose of this study is to compare self-management of diabetes pre-COVID-19 and during the COVID-19 pandemic. Methods 679 participants with diabetes completed an online structured questionnaire survey. Various exposure variables (demographics, duration, treatment and complications of diabetes, self-isolation, etc.) were analysed to examine associations with the following outcome variables: (i) fluctuation of blood glucose levels, (ii) access to diabetes medicine, (iii) access to healthy diet, (iv) physical activity. Adjusted multiple regression analysis ascertained significant associations for each outcome variable against exposure variables. Results Multiple regression analysis showed that self-isolation was significantly associated with greater fluctuation in blood glucose levels (OR = 1.8, 95% CI = 1.2–2.6, p = 0.005), reduced access to diabetes medicine (OR = 1.9, 95% CI = 1.1–3.1, p = 0.02) and reduced access to healthy diet (OR = 3.0, 95% CI = 2.0–4.6, p < 0.001). Fluctuation in blood glucose level was also significantly associated with having at least one complication of diabetes (OR = 2.2, 95% CI = 1.2–3.9, p = 0.008) and reduced access to diabetes medicine was significantly higher in people who were on insulin (OR = 2.1, 95% CI = 1.3–3.3, p = 0.001). Conclusions Self-isolation was shown to impact almost all factors that influence self-management of diabetes. A targeted approach to improved access to diabetes medicine, healthy diet for people who needed to self-isolate is vital in order to ensure that they are able to self-manage their diabetes effectively.