Joint fluid aspiration, or arthrocentesis, is one of the most useful and commonly performed procedures for the diagnosis and treatment of rheumatic diseases, but to date no definite guidelines have been published. For this reason, a group of experts of the Italian Society of Rheumatology (SIR) produced evidence based recommendations for performing arthrocentesis. Among them, the most relevant are: a) arthrocentesis is necessary when synovial effusion of unknown origin is present, especially if septic or crystal arthritis is suspected; b) the patient should be clearly informed of the benefits and risks of the procedure in order to give an informed consent; c) ultrasonography should be used to facilitate arthrocentesis in difficult joints; d) fluid evacuation often has a therapeutic effect and facilitates the success of the following intraarticular injection; e) careful skin disinfection and the use of sterile, disposable material is mandatory for avoiding septic complications. Disposable, non sterile gloves should always be used by the operator, mainly for his own protection; f) contraindications are the presence of skin lesions or infections in the area of the puncture; g) the patient's anticoagulant treatment is not a contraindication, providing the therapeutic range is not exceeded; h) joint rest after arthrocentesis is not indicated. Several of these recommendations were based on experts' opinion rather than on published evidence which is scanty.