The primary purpose was to determine the underlying structure of the vulnerable infant's response to an acute painful procedure. The secondary purpose was to explore the influence of context (e.g., risk for neurological impairment [NI] and gestational age [GA]). A descriptive cohort design determined contributions of selected indicators to the structure of infant pain. The magnitude of variance for 19 pain indicators was assessed using 3 exploratory factor analyses in 149 neonates. The basic exploratory factor structure included behavioural (e.g., facial actions) and physiological (e.g., oxygen saturation, heart rate) indicators. Facial actions accounted for the greatest variance across all factor solutions (29-39%). Physiological indicators explained 8 to 26% additional variance. There were no consistent differences in the factor structures when contextual factors were explored.