Abstract Background Recombinant granulocyte-colony stimulating factor (G-CSF) mobilized pluripotent cells from the bone marrow are proposed to have a regenerative potential. Though, a report of excessive instent restenosis, in patients treated with G-CSF before percutaneous coronary intervention (PCI) warrants caution. Methods Patients ( n = 59) enrolled in the STEMMI trial, a randomized and double blind study, comparing G-CSF and placebo after large ST-elevation myocardial infarctions, had an intracoronary ultrasound imaging at 6 months follow-up with a quantitative analysis of instent neointimal hyperplasia. Results During G-CSF treatment leukocyte counts, and CD34+ and CD45−/CD34− cell fractions in peripheral blood increased markedly ( p < 0.0001 vs. placebo). At follow-up, there were no differences in intracoronary late lumen loss, expressed as neointima volume per mm of stent (1.6 mm3 ± 1.2 G-CSF group vs. 1.9 mm3 ± 1.3 placebo group; p = 0.38), and in minimal instent lumen area (5.4 mm2 ± 2.4 vs. 5.3 mm2 ± 2.6, p = 0.90). In the placebo group, plasma concentration of stromal cell-derived factor-1 (SDF-1) increased significantly after STEMI. This SDF-1 response was completely suppressed during G-CSF treatment. A rebound increase of SDF-1 was observed after withdrawal of G-CSF ( p = 0.001). Plasma concentration of SDF-1 at the time of stent implantation correlated positively to neointimal hyperplasia ( p = 0.025). Conclusions G-CSF treatment, initiated after PCI, does not lead to excessive instent neointimal hyperplasia or restenosis in patients with STEMI. The timing of G-CSF, in relation to the PCI, might be important, as G-CSF influences SDF-1.