Acute respiratory infection is a common reason for people to present for medical care. Advice to increase fluid intake is a frequent treatment recommendation. Attributed benefits of fluids include replacing increased insensible fluid losses, correcting dehydration from reduced intake and reducing the viscosity of mucus. However, there are theoretical reasons for increased fluid intake to cause harm. Anti-diuretic hormone secretion is increased in lower respiratory tract infections of various aetiologies. This systematic examination of the evidence sought to determine the benefit versus harm from increasing fluid intake. To answer the following questions.1. Does recommending increased fluid intake as a treatment for acute respiratory infections improve duration and severity of symptoms? 2. Are there adverse effects from recommending increased fluids in people with acute respiratory infections? 3. Are any benefits or harms related to site of infection (upper or lower respiratory tract) or a different severity of illness? We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, issue 4), which contains the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to November Week 3, 2010), EMBASE (1974 to December 2010), Current Contents (2000 to December 2010) and CINAHL (1982 to December 2010). We searched reference lists of articles identified and contacted experts in the relevant disciplines. Randomised controlled trials (RCTs) that examined the effect of increasing fluid intake in people with acute respiratory infections. Two review authors independently assessed the identified studies to determine eligibility for inclusion. No RCTs assessing the effect of increasing fluid intake in acute respiratory infections were found. There is currently no evidence from RCTs for or against the recommendation to increase fluids in acute respiratory infections. The implications for fluid management of acute respiratory infections in the outpatient or primary care setting have not been studied in any RCTs to date. Some non-experimental (observational) studies report that increasing fluid intake in acute respiratory infections of the lower respiratory tract may cause harm. RCTs need to be done to determine the true effect of this very common medical advice.