Objective The aim of this study was to evaluate the importance of growth-differentiation factor-15 level and tissue Doppler imaging in the detection of cardiomyopathy in children who have type 1 diabetes mellitus. Materials and Methods Thirty-eight patients (11 males and 27 females) with type 1 diabetes mellitus were included in this study. The control group consisted of 40 age- and gender-matched healthy volunteers. All children underwent a detailed echocardiography, which contained an m-mode, pulse Doppler and tissue Doppler imaging; and growth-differentiation factor-15 level was measured. Results In this study, there were significant differences between diastolic function parameters of the heart. The mitral isovolumic contraction time, contraction time, and isovolumic relaxation time values were different in the patients than in the controls (p < 0.01, p < 0.01, p < 0.01, respectively). Also, the tricuspid isovolumic contraction time, contraction time, and isovolumic relaxation time values were different in the patients than in the controls (p < 0.01, p = 0.01, p < 0.01, respectively). No statistically significant difference was found between the other M-mode parameters. Mean plasma growth-differentiation factor-15 level was significantly higher in patients than in healthy controls (p < 0.01). Conclusion The follow-up of children with type 1 diabetes mellitus in terms of cardiomyopathy and the use of tissue Doppler imaging and growth differentiation factor-15 levels may be useful.