Knee ultrasound is a very useful tool for the clinical examination of rheumatic patients. In the last years many papers have been focused on this subject, exhibiting a high degree of improvement since the first musculoskeletal ultrasound paper concerning the knee was published 30 years ago. Apart from the accurate description of anatomic landmarks and structures and also of the basic pathological findings (fluid, synovitis, enthesitis, osteophytes), rheumatologic research has focused on inflammatory findings quantification and their reaction to remissive treatments. The aim of this review is to describe the normal ultrasonographic appearance of knee structures concisely and mainly to analyse the literature about pathological findings in the knee joint.