Automatic tissue segmentation tools are common in the neuroimaging field. Evaluating their reliability is necessary to validate the findings of studies that use these tools. We conducted a reliability analysis for SIENAX in a test-retest dataset and a multi-site dataset. The results were analysed and compared with other automatic segmentation tools. The volumetric outputs of SIENAX show low coefficients of variance for the test-retest dataset in both grey matter (1.11%) and white matter (0.69%). In the multi-site data the results were to 3.95% and 6.47% respectively, suggesting a possible need for data harmonization in multi-site studies.