The objective was to determine the level of knowledge on diabetes in an adult population in Turkey. In this cross-sectional study, 524 people aged over 30 were selected from the population of Narlıdere Health District, Izmir, Turkey. A questionnaire was performed to determine sociodemographic characteristics and knowledge of diabetes. Each item on the questionnaire was given a score with a possible final total of 100 points. Knowledge level was evaluated in the whole group, DM-positive and -negative groups. “DM-positive” group refers to respondents who either have diabetes themselves or whose relatives have it. “DM-negative” group refers to respondents who do not have diabetes themselves and whose relatives do not. In total, 479 people were included in the study (response rate=87.6%). The mean age of the study group was 50.2±12.8 and 61% of them were women. Mean diabetes knowledge scores were 62.9±17.9 for the study group, 68.3±16.1 for the “DM-positive” group and 60.6±18.2 for the “DM-negative” group. The “DM-negative” group had a significantly lower mean score than the other two groups. Overall, diabetes knowledge was higher in participants with diabetes or who had a relative with diabetes, who were educated for more than 5 years and who had health insurance. The diabetes knowledge of the study group was not satisfactory. Diabetics and people who have relatives with diabetes had a higher knowledge level than the population without diabetes. Detailed information regarding diabetes should be provided to not only diabetics, but also the population as a whole.