Background: Infants in NICU are exposed to repeated, invasive procedures resulting in acute or chronic pain that may predispose to significant clinical, physiologic and psychologic sequelae. Aim: To assess pain response in newborns after endotracheal intubation and umbilical vein catheterization using multidimensional measurements. Study Design and method: 75 preterm and term newborns were involved in our non-randomized controlled prospective study. They were classified into 3 groups: group A (N=30) included newborns exposed to intubation, group B (N=15) included newborns underwent insertion of umbilical vein catheterization and the control newborns (N=30) of matched age & sex. Our assessment included measurements of physiological indicators (HR, RR, MAP, SaO2 and palmar sweating), behavioral indicators (facial expression: brow bulge, nasolabial furrows, mouth opening and grimace, body movements and crying). and hormonal indicators (plasma renin activity). Result: Regarding group A There was significant increase of HR, MAP, SaO2 and PRA and significant decline of RR after intubation. concerning group B there was no statistical significant difference of HR, RR, MAP and SaO2 after catheterization. however, there was significant increase of PRA after umbilical vein catheterization. There was significant increase of physiological, behavioral & hormonal indicators in both groups A & B when compared to control group. We found a statistical significant correlation between post-intubation PRA and MAP. PRA was found to be the single indicator of pain in group A. On the other hand, we did not find any reliable indicator of pain group B. Conclusion: neonates show variable physiological, behavioral and hormonal responses to different procedures in NICU according to the severity of pain. We need tailored tools for assessment of pain according to both underlying illness and severity of disease.