Background: Granulocyte colony stimulating factor (G-CSF) is a naturally-occurring cytokine that has been shown to increase neutrophil function and number. Exogenous administration of recombinant G-CSF (filgrastim, pegfilgrastim or lenograstim) has found extensive use in the treatment of febrile neutropenia, but its role in the treatment of infection in non-neutropenic hosts is less well defined. Objectives: We explored the role of G-CSF as an adjunct to antibiotics in the treatment of pneumonia in non-neutropenic adults. Search strategy: For this updated review we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 4, 2006); MEDLINE (1950 to January 2007); EMBASE (1988 to January 2007); and online databases of clinical trials (www.controlledtrials.com, updated 10 November, 2006). Selection criteria: We considered randomized controlled trials (RCTs) which included hospitalized adult patients with either community-acquired pneumonia or hospital-acquired pneumonia. Data collection and analysis: Two review authors independently extracted data and assessed trial quality. The primary outcome measure was 28-day mortality. Secondary outcome measures included other markers of mortality as well as markers of adverse events, including organ dysfunction. An assessment of methodological quality was made for each study. Main results: Six studies with a total of 2018 people were identified. G-CSF use appeared to be safe with no increase in the incidence of total serious adverse events (pooled odds ratio (OR) 0.91; 95% confidence interval (CI): 0.73 to 1.14) or organ dysfunction. However, the use of G-CSF was not associated with improved 28-day mortality (pooled OR 0.81; 95% CI: 0.52 to 1.27). Authors' conclusions: There is no current evidence supporting the routine use of G-CSF in the treatment of pneumonia. Studies in which G-CSF is administered prophylactically or earlier in therapy may be of interest.