Conciousness is decisive in attributing meanings to the manifestations of life. The impact of diabetes mellitus on patients` psychic and psychosocial functionality depends on the understanding of the disease. Objective: to study the dynamics of changes in psychic and psychosocial functionality in patients with diabetes mellitus, before and after diagnosis. Participants: 50 subjects of both sexes, with diabetes mellitus (30 - 88 years) and 50 subjects with the same socio-demographic characteristics, who do not suffer from the disease. Methodology: Clinical-psychological interview; Socio-demographic questionnaire; Clinical-dynamic disease questionnaire; Self-assessment questionnaire on psychic, family, social and work functionality. Results: Diabetes mellitus patients in the period of life “after diagnosis”, compared to the period “before diagnosis”, show statistically significant differences of greater expressiveness psychic functionality (nervousness, anxiety, irritability, depression, pessimism and fatigue) and lower in psychosocial and work activities (work capacity, availability to socialize with friends and family). In the comparison “before diagnosis” and “current moment” there are significant differences in all categories, but if comparing “after diagnosis” and “current moment”, significant differences only exist in work capacity, fatigue, availability to live together with friends; lower values at the present time. Conclusion: The intrusion of diabetes mellitus and the patient's knowledge of the diagnosis cause changes in the dynamics of psychic functionality and psychosocial activity, aggravating the levels of nervousness, anxiety, irritability, depression, pessimism, feeling of fatigue, less work capacity, availability to socialize with friends and family. Diabetes has a negative impact on the functionality of patients, affecting well-being and quality of life.