Objective: Determine association between time to regain birthweight and 2-year neurodevelopment among extremely preterm (EP) newborns.Study design: Secondary analysis of the Preterm Erythropoietin Neuroprotection Trial evaluating time to regain birthweight, time from birth to weight nadir, time from nadir to regain birthweight, and cumulative weight loss with 2-year corrected Bayley Scales of Infant and Toddler Development 3rd edition.Results: Among n = 654 EP neonates, those with shorter nadir-to-regain had lower cognitive scores (≤1 day versus ≥8 days: −5.0 points, [CI −9.5, −0.6]) and lower motor scores (≤1 day versus ≥8 days: −4.6 points [CI −9.2, −0.03]) in adjusted stepwise forward regression modeling. Increasingly cumulative weight loss was associated with lower cognitive scores (≤−50 percent-days: −5.6, [CI −9.4, −1.8]), motor scores (≤−50 percent-days: −4.2, [CI -8.2, -0.2]); and language scores (≤−50 percent-days: −6.0, [CI −10.1, −1.9]).Conclusion: Faster nadir-to-regain and excessive cumulative weight loss are associated with adverse 2-year neurodevelopmental outcomes.Trial registration: PENUT Trial Registration: NCT01378273. https://clinicaltrials.gov/ct2/show/NCT01378273.Clinical trial registration: This study is a post-hoc secondary analysis of pre-existing data from the PENUT Trial (NCT #01378273).