Diabetes mellitus is a civilization disease which affects increasing number of people. Diabetes essentially influences gingival disease, periodontal disease, saliva secretion disorders and its parameters. The aim of the study is both assessing the oral cavity status of that group of patients to clearly identify their treatment needs and the effectiveness of implementation of oral hygiene training. 57 patients with type 1 diabetes and 31 healthy declared their contribution to the research. The research was conducted within two visits. The evaluation was done during clinical examination: teeth condition, oral hygiene. During the end of the first visit patients received professional oral hygiene instructions. Analysis of the clinical research in both groups showed no differences for Decayed- Missing- Filled teeth index and Dental Treatment Index. The results demonstrated disparity between the groups for the decayed teeth component and filled teeth component (symptomatically higher values in the researched group). There was statistically significant difference in the modified Sulcus Bleeding Index values analysis between both groups. Conducting hygiene instructions influenced the decline of Approximal Plaque Index and Oral Hygiene Index in the treatment group. It is essential for dentists in cooperation with diabetologists to educate patients on the necessity to maintain oral hygiene procedures. Keywords: diabetes mellitus; oral hygiene; chronic disease; dental treatment needs