BACKGROUND Since the introduction of randomized controlled trials (RCT) in clinical research, there has been discussion of whether enrolled patients have worse or better outcomes than comparable non-participants. OBJECTIVE To investigate whether very preterm infants randomized to a placebo group in an RCT have equivalent neurodevelopmental outcomes to infants who were eligible but not randomized (eligible NR). METHODS In the course of an RCT investigating the neuroprotective effect of early high-dose erythropoietin on the neurodevelopment of very preterm infants, the outcome data of 72 infants randomized to placebo were retrospectively compared with those of 108 eligible NR infants. Our primary outcome measures were the mental (MDI) and psychomotor (PDI) developmental indices of the Bayley Scales of Infant Development II at 24 months of corrected age. The outcomes of the two groups were considered equivalent if the confidence intervals (CIs) of their mean differences fitted within our ±5-point margin of equivalence. RESULTS Except for a higher socioeconomic status of the trial participants, both groups were balanced for most perinatal variables. The mean difference (90% CI) between the eligible NR and the placebo group was -2.1 (-6.1 and 1.9) points for the MDI and -0.8 (-4.2 and 2.5) points for the PDI. After adjusting for the socioeconomic status, maternal age and child age at follow-up, the mean difference for the MDI was -0.5 (-4.3 and 3.4) points. CONCLUSIONS Our results indicate that the participation of very preterm infants in an RCT is associated with equivalent long-term outcomes compared to non-participating infants. © 2014 S. Karger AG, Basel.