We compared the rates of fever in adult subjects with laboratory-confirmed influenza and other respiratory viruses and examined the factors that predict fever in adults. Symptom data on 158 healthcare workers (HCWs) with a laboratory-confirmed respiratory virus infection were collected using standardized data collection forms from three separate studies. Overall, the rate of fever in confirmed viral respiratory infections in adult HCWs was 23.4% (37/158). Rates varied by virus: human rhinovirus (25.3%, 19/75), influenza A virus (30%, 3/10), coronavirus (28.6%, 2/7), human metapneumovirus (28.6%, 2/7), respiratory syncytial virus (14.3%, 4/28) and parainfluenza virus (8.3%, 1/12). Smoking [relative risk (RR) 4.65, 95% confidence interval (CI) 1.33-16.25] and co-infection with two or more viruses (RR 4.19, 95% CI 1.21-14.52) were significant predictors of fever. Fever is less common in adults with confirmed viral respiratory infections, including influenza, than described in children. More than 75% of adults with a viral respiratory infection do not have fever, which is an important finding for clinical triage of adult patients with respiratory infections. The accepted definition of \'influenza-like illness\' includes fever and may be insensitive for surveillance when high case-finding is required. A more sensitive case definition could be used to identify adult cases, particularly in event of an emerging viral infection.