Purpose: The 1-repetition maximum (1-RM) test is the gold standard test for evaluating maximal dynamic strength of groups of muscles. However, safety of actual 1-RM testing is questionable in clinical situations such as type 2 diabetes (T2D), where an estimated 1-RM test is preferred. It is unclear if acceptable test retest reliability exists for the estimated 1-RM test in middle aged T2D patients. This study examined the reliability of the estimated 1-RM strength test in untrained middle aged T2D subjects.Methods: Twenty five untrained diabetic males (n=19) and females (n=6) aged 40.7+0.4 years participated in the study. Participants undertook the first estimated 1-RM test for five exercises namely supine bench press, leg press, lateral pull, leg extension and seated biceps curls. A familiarisation session was provided three to five days before the first test. 1-RM was estimated for all participants by Brzycki 1-RM prediction equation. Another identical 1-RM estimation procedure occurred one week after first test. Intraclass correlation coefficients (ICC), paired t-test, standard error of measurement (SEM), BlandAltman plots, and estimation of 95% CI were used to assess reliability.Results: Test-retest reliability was excellent (ICC 2,1 =0.98-0.99) for all measurements with the highest for leg extension (ICC 2,1 =0.99). The SEM was lowest for lateral pull and leg extension exercises. Paired t-tests showed nonsignificant differences between the means of 2 sessions across three of five exercises. Conclusions:The study findings suggest that estimation of 1-RM is reliable for upper and lower body muscular strength measurement in untrained middle aged T2D patients.