Background The rate of laboratory test utilisation has been increasing unsustainably. Evaluating inappropriately repeated laboratory tests is promising because objective criteria are available to measure the rates while causes can be manipulated easily. In this study, we aimed to evaluate the prevalence, associated factors and financial burden of inappropriate repeat tests. Methods A cross-sectional study was conducted on the results of 26 types of laboratory tests recorded in a laboratory database of a tertiary hospital between 1 July 2014 and 30 June 2017. Minimum retest intervals were determined from the literature for each type of tests. If the time interval between the two tests was shorter than the minimum retest interval, then the later test was accepted an inappropriate repeat test. Binary logistic regression was performed after univariate analyses. Results Of a total of 673 794 tests, 109 370 (16.2%) were inappropriate repeat tests. Male gender, being >= 65 years old, being an inpatient, high-volume test and surgical clinic as the test-requesting clinic were associated with inappropriate repeat tests. Also, it was determined that US$66 761.3 had been wasted on inappropriate repeat tests for 3 years. Discussion There are several factors that increase the rate of inappropriate repeat tests. They should be considered during health policy making or planning interventions to reduce inappropriate repeat tests.