To compare outcomes of single-fraction and multi-fraction stereotactic ablative body radiotherapy (SABR) for pulmonary metastases.A retrospective review from two academic institutions of patients with one to three pulmonary metastases staged with (18)F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) scans. For single-fraction SABR, 26 Gy was prescribed for peripheral targets and 18 Gy for central targets. In the multi-fraction cohort, 48 Gy/4 or 50 Gy/5 was prescribed for peripheral targets and 50 Gy/5 was prescribed for central targets. Three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans were delivered using heterogeneity corrections. Conformity indices at an intermediate dose (R50%) and at a high dose (R100%) were used to assess a relationship with the planning target volume (PTV). Overall survival, local and distant progression and toxicity rates were analysed from the date of treatment completion.Between February 2010 and June 2013, 65 patients with 85 pulmonary metastases were reviewed. The median follow-up was 2.1 years. Metastases most commonly originated from colorectal cancer (31%), followed by non-small cell lung cancer (25%). 3D-CRT was used in 52 targets, IMRT in 21 and VMAT in 12. 3D-CRT showed a lower median R50% (P=0.01), but a higher median R100% than IMRT/VMAT (P=0.04). The R50% index was inversely correlated to the PTV with all techniques (P=0.01). Overall survival at 1 and 2 years in all patients was 93% (95% confidence interval 87-100%) and 71% (95% confidence interval 58-86%), respectively. The 2 year freedom from local and distant progression was 93% (95% confidence interval 86-100%) and 38% (95% confidence interval 27-55%), respectively. There were no significant differences between overall survival (P=0 .14), time to distant progression (P=0.06) or toxicity rates (P=0.75) between single- and multi-fraction cohorts.We report comparable local control, overall survival and toxicity rates between single-fraction and multi-fraction SABR treatments in patients with FDG-PET-staged pulmonary oligometastases. We propose a guideline for R50% conformity incorporating 3D-CRT/IMRT/VMAT techniques with heterogeneity corrected planning algorithms.