Background Distinguishing peritonsillar abscess (PTA) from peritonsillar cellulitis using clinical assessment is challenging as many features overlap for both conditions, and physical examination is only about 75% sensitive and 50% specific for diagnosing PTA. The primary objective of this systematic review was to determine the test characteristics of ultrasound for diagnosing PTA when compared to a reference standard of computed tomography or acquisition of pus via needle aspiration or incision and drainage. Methods This systematic review was performed in accordance with the Preferred Reporting Items for a Systematic Review and Meta‐analysis of Diagnostic Test Accuracy (PRISMA‐DTA) guidelines. We searched seven databases from 1960 to November 2022. Two independent reviewers completed study selection, data extraction, and QUADAS‐2 risk‐of‐bias assessment. We used a bivariate random‐effects model to calculate pooled sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR–). We also conducted subgroup analyses on radiology ultrasound compared to point‐of‐care ultrasound (POCUS) and intraoral compared to transcervical scanning techniques. Results From 339 citations, we identified 18 studies for inclusion. Because one study only reported positive cases of PTA (thereby preventing the calculation of specificity), it was excluded from the analysis, so the analysis included a total of 17 studies with 812 patients, of whom 541 had PTA. Pooled bivariate sensitivity was 86% (95% confidence interval [CI] 78%–91%), specificity 76% (95% CI 67%–82%), LR+ 3.51 (95% CI 2.59–4.89), and LR– 0.19 (95% CI 0.12–0.30). On subgroup analysis, radiology‐performed ultrasound had a sensitivity and specificity of 89% and 71%, compared to POCUS, which had a sensitivity and specificity of 74% and 79%. Comparing the two different techniques, intraoral had a sensitivity and specificity of 91% and 75% while transcervical had a sensitivity and specificity of 80% and 81%. Conclusions Ultrasound demonstrates high sensitivity for ruling out PTA, but it only has moderate specificity for ruling in the diagnosis.