ABSTRACT Although it is a severe complication in immunocompromised patients, diagnosing invasive fungal disease (IFD), especially invasive aspergillosis (IA), remains difficult. In certain clinical scenarios, examining tissue samples for identification of the infectious organism becomes important. As culture-based methods rarely yield results, the performance of an Aspergillus -specific nested PCR in fresh tissue or pleural effusion samples was evaluated. Fresh tissue ( n = 59) and effusion ( n = 47) specimens from 79 immunocompromised patients were subjected to an Aspergillus -specific PCR assay. Twenty-six patients had proven ( n = 20) or probable ( n = 6) IFD, according to the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) criteria, while the remaining patients were classified as having either possible IFD ( n = 30) or no IFD ( n = 23). IA was identified as the underlying IFD in 21/26 proven/probable cases. PCR positivity was observed for 18/21 proven/probable and 6 possible IA cases; cases classified as no IA did not show positive signals. Patients with proven IFD ( n = 5) with cultures positive for non- Aspergillus molds also had negative Aspergillus PCR results. Aspergillus PCR performance analysis yielded sensitivity and specificity values of 86% (95% confidence interval [CI], 65% to 95%) and 100% (95% CI, 86% to 100%), respectively, thus leading to a diagnostic odds ratio of >200. In this analysis, good diagnostic performance of the PCR assay for detection of IA was observed for tissue samples, while effusion samples showed lower sensitivity rates. PCR testing represents a complementary tool; a positive PCR result strengthens the likelihood of IA, whereas IA seems unlikely in cases with negative results but findings could indicate non- Aspergillus IFD. Thus, PCR testing of these specimens enhances the diagnostic capabilities.