OBJECTIVETo examine the effects of clinicians' provision of (un)reasonable arguments on parent-related outcomes in neonatal (intensive) care (NICU), starting from the NICU Communication Framework.METHODSA video-vignette experiment, in which we systematically varied clinicians' use of (reasonable, unreasonable, no) argumentation across two non-acute and two acute decision-making scenarios (3×4 design). Reasonable arguments were medically appropriate and constructive reasons to support the treatment plan, as defined by an expert panel. Based on argumentation theory, unreasonable arguments included hindering appeals to authority or the self-evident nature of the treatment plan. Parents of preterm infants completed an online survey, viewing 1 of 12 video-vignettes and answering questions pertaining to their communication stress, understanding, agreement, participation in communication, empowerment, trust and satisfaction with communication.RESULTSN = 163 parents completed the full survey. We found statistically significant (p < 0.001) and large (η2: 0.13-0.38) effects of clinicians' use of argumentation across all parent-related outcomes. Reasonable argumentation led to lower communication stress and higher understanding, agreement, participation in communication, empowerment, trust, and satisfaction with communication than no argumentation. In turn, no argumentation led to improved outcomes compared to unreasonable argumentation. This pattern was similar across non-acute and acute scenarios.CONCLUSIONClinicians' use of reasonable argumentation has a consistently strong and positive impact on parent-related outcomes in neonatal care.PRACTICE IMPLICATIONSWe argue that reasoned decision-making should be considered a good clinical practice, core to patient-centered communication. Our findings provide a starting point for (1) determining good argumentative practices and (2) designing evidence-based clinical argumentation trainings.