Background Malignant pleural effusion (MPE) greatly influences clinical management and therapeutic decision-making in patients with cancer. Accurate differentiation between MPE and non-MPE is therefore essential. This study aimed to evaluate the diagnostic accuracy of traditional ultrasonographic signs and ultrasound findings of adjacent thoracic structures in identifying MPE. Methods PubMed, Scopus, Web of Science, and Embase were searched until 02 May 2025 to identify studies evaluating the diagnostic accuracy of ultrasonographic signs using TrUS and SWE for detecting MPE. Pooled sensitivity, specificity, diagnostic odds ratio, predictive values, and likelihood ratios were estimated using a random-effects model. Results Ten studies fulfilled the eligibility criteria, including nine evaluating TrUS and three investigating SWE. Several ultrasonographic signs were highly specific for MPE, including pleural nodules (99%), diaphragmatic nodules (96%), and pleural thickening (93%). Concomitant chest wall invasion, hepatic metastasis, and lung consolidation showed near-absolute specificity (99–100%). Nevertheless, the sensitivity of these signs did not exceed 60%. Meanwhile, SWE showed balanced diagnostic performance, with sensitivity ranging from 76.36% to 100% and specificity ranging from 59.09% to 94.40%, depending on the cutoff values used. Conclusion TrUS can be considered in the working diagnosis of MPE, as pleural and diaphragmatic nodules, pleural thickening, chest wall invasion, lung involvement, and liver metastasis show high specificity for MPE. However, further studies are needed to investigate the role of SWE in diagnosing MPE.