To investigate and characterise general and diabetes-specific worries related to COVID-19 among people with diabetes in Denmark during the first 3 months of the pandemic. In a longitudinal study from March to June 2020, six online questionnaires (Q1-Q6) were distributed to 2430 adult members of two diabetes panels. Worries related to COVID-19 were measured with closed- and open-ended items. Data from closed-ended items were analysed descriptively. Open-ended responses were analysed with systematic text condensation. Using chi-squared tests, changes in proportions of worries over time were analysed, and differences in diabetes-specific worries by gender and diabetes diagnosis were explored. At Q1, 1366 individuals returned a response (Q2: 1082, Q3: 992, Q4: 977, Q5: 901, Q6: 816). In the beginning of the pandemic, 2 weeks after the first lockdown in Denmark, the most frequently reported general worries related to someone close becoming seriously ill, changes in daily life such as limitations on social interactions and uncertainty about the duration of those changes. The most frequently reported diabetes-specific worries were about severity of illness with COVID-19 due to diabetes, being identified as a member of a group at risk for COVID-19 and being unable to manage diabetes if ill with COVID-19. All concerns decreased over 3 months, as the society gradually reopened, except for persistent worries about being able to manage diabetes if ill with COVID-19. More women and people with type 1 diabetes reported worries, compared with men and people with type 2 diabetes. Our study highlights the diversity of worries related to the COVID-19 pandemic among people with diabetes and changing patterns of worry over time and across subgroups as the society reopened in Denmark. These insights can be helpful when providing support for people with diabetes during health crises.