Introduction: A positive interferon-gamma release assay (IGRA) is regarded as proof of latent Mycobacterium tuberculosis infection. We conducted an evaluation of the IGRA test "T-SPOT.TB" to test its performance during clinical routine use by analysing the positivity rate and odds, effect of season and sensitivity. Material And Methods: Data from T-SPOT.TB testing together with age and test indications (anti-tumour necrosis factor alpha (TNFα) candidate, contact investigation or suspicion of tuberculosis (TB)) were combined with mycobacteria culture results. RESULTS: A total of 1,809 patients were tested. Conclusive results were achieved for 1,780 patients (98.4%). Among these, 4.6% of anti-TNFα candidates, 19.3% of contacts and 24.4% of TB suspects tested positive. Compared with anti- TNFα candidates, the odds for a positive result were significantly higher for contact investigations (odds ratio (OR), mean (95% confidence interval): 4.93 (3.11-7.81)) and TB suspects (OR: 6.83 (4.33-10.77)). Elevated odds of an inconclusive test were found during autumn and winter periods (OR: 2.53 (1.58-4.05)) and for patients > 75 years of age (OR: 2.66 (1.43-4.94)) and < 6 years of age (OR: 3.35 (1.58- 7.09)). In all, 41 of 43 culture-verified M. tuberculosis infections tested positive with one false negative. Conclusion: During routine testing, inconclusive tests were rare, but more frequent during autumn/winter periods and for patients < 6 and > 75 years of age. The TSPOT. TB showed a high sensitivity in culture-verified TB, although false negative results did occur.