Aerosolised administration of antibacterials remains theoretically attractive for the prevention and treatment of hospital-acquired pneumonia (HAP) because of the ability to generate high drug concentrations at the site of infection. There is renewed interest in this area because of the shortcomings of current therapies and increasing multidrug resistance in Gram-negative organisms. Clinical trials of aerosolised or endotracheally administered antibacterials for HAP prevention have generally been positive; however, early trials were hampered by the development of resistance related to indiscriminate use. More recent trials have shown efficacy at HAP prevention without adverse effects on microflora as a result of more limited usage. However, prophylactic aerosolised antibacterials still need to be studied in large randomised trials before they could enter widespread use. The treatment of HAP with aerosolised antibacterials has mostly been reported in case series without control groups. Both early reports with aminoglycosides and the more recent use of colistin have reported very good response rates; even with organisms such as Pseudomonas aeruginosa and Acinetobacter baumannii. Aerosolised antibacterials were almost always added to intravenous therapy. On the basis of these reports, the current HAP guidelines allow the addition of aerosolised antibacterials in selected patients with multidrug-resistant organisms. This seems to be a reasonable recommendation until large trials are performed. Overall, toxicity was relatively low in the publications reviewed. Aerosolised drug administration in mechanically ventilated patients requires attention to a number of factors in order to maximise drug deposition in the lung.