Purpose To compare the intraoperative complications between 23-G and 20-G instrumentation in patients undergoing pars plana vitrectomy (PPV). Methods This was a retrospective comparative study of 4,274 PPV procedures by the same surgical team between 1998 and 2016. A total of 2,648 operations were carried out with 20-G surgery and 1,626 operations with 23-G surgery. Main outcome measures were the incidence of choroidal haemorrhage, iatrogenic retinal break, and lens touch. Results The most frequent surgical indication in both 20-G and 23-G was rhegmatogenous retinal detachment (RRD), 38.7% (1,026/2,648) and 45.9% (746/1,626), respectively. The frequency of choroidal haemorrhage was 1.0% with 20-G surgery (26/2,648) vs 0.6% with 23-G (9/1,626, p = 0.16). Subgroup analysis showed the increased risk was present in RRD surgery, 1.6% (16/1,026) vs 0.1% (1/746, p = 0.002), but not in all other indications combined, 20-G with 0.6% (10/1,622) and 23-G 0.9% (8/88, p = 0.46). This increased risk was also true for RRD when excluding combined scleral buckle surgery. There was an increased risk of iatrogenic retinal break in RRD cases undergoing 20-G, 5.8% (60/1,026), compared to 23-G vitrectomy, 1.9% (14/746, p<0.0001). There was no difference in rates of lens touch between 20-G and 23-G. Conclusions 23-G microincisional PPV has a lower risk of choroidal haemorrhage and iatrogenic retinal tears than 20-G vitrectomy particularly for eyes with RRD.