Background:Knee cysts are common clinical findings and MRI is frequently used in their assessment. However, compared to ultrasound (US), MRI is expensive and of limited availability. The objective of the current study is to compare the efficacy of US and MRI in the detection and characterization of benign cysts and cyst-like lesions in and around the knee with a gold standard correlation. Patients and methods. Patients with benign cysts or cyst-like lesions in or around the knee were included. All patients underwent MRI followed by US of the affected knee. Based on the gold-standard correlation, the diagnostic performances of both imaging modalities in each type of cystic lesion were quantified and compared. Finally, the agreement between each imaging modality and the gold standard and between both modalities was calculated. Results.The diagnosis of benign knee cystic lesions was confirmed in 96 patients. Baker's cyst was the most frequent followed by meniscal and ganglion cysts. There was a predominance of males, young and middle-aged, and right knee affection. MRI showed insignificantly higher accuracies (100%, 100%, and 99%) than those of US (97%, 95.8%, and 97%) in diagnosing Baker's, meniscal, and ganglion cysts (p < /em>>0.05). The agreement between MRI and US was substantial regarding the detection of ganglion cysts (k=0.75), and almost perfect regarding Baker's and meniscal cysts (k=0.96 and 0.90). Conclusion.US is a time- and cost-effective, easily available, and non-invasive imaging modality with comparable accuracy to MRI in diagnosing benign knee cysts and cyst-like lesions. However, US is of limited performance as regards small parameniscal and intra-articular ganglion cysts.