Diabetes mellitus is a long-term metabolic illness that affects people's social, physical, mental, and psychological health and can have a tremendous impact on the handwriting of an individual. Examining such handwriting specimens might be difficult for document examiners. This may have an effect on the reliability of their opinions on the subjects under consideration. As a result, the present study has been conducted to qualitatively and quantitatively determine the effects of diabetes mellitus on handwriting characteristics. A qualitative examination and comparative analysis of line quality errors in altered writings and writings copied by diabetes mellitus were also included in the study.