The use of oseltamivir at mass gatherings (MGs) or other crowded settings has not previously been systematically examined to synthesise the evidence of its usefulness. Here we have evaluated its effectiveness by reviewing the published literature. The effectiveness of oseltamivir at MGs is controversial because published clinical trials evaluating this are lacking. Its use, to date, has been predominantly therapeutic, i.e. to treat patients with confirmed or suspected influenza. There are some examples of its use in mass prophylaxis at MGs and other crowded settings like schools and camps, and closed settings such as prisons and aged care facilities. Most of the available studies indicate that oseltamivir use, whether therapeutic or prophylactic, is effective in containing influenza outbreaks in those settings though there are some reports of moderately high side effects, particularly among young children. Targeted prophylaxis of oseltamivir seems to help contain an outbreak of influenza at MG. A combination of 'treatment of cases' and 'ring prophylaxis of contacts' appears to be a feasible and economically sustainable strategy. Further research needs to be directed to uncertainties (e.g. how, when and for whom oseltamivir should be used) over oseltamivir's place in influenza control at mass gatherings.