Background: Five Korotkoff phases are described in adults, but there are no studies of the Korotkoff phase distribution in children. This study determines the presence and length of Korotkoff phases in children, providing data on the repeatability of these measurements, the relationship between the phases, and finally the relationship between the phases and heart rate, blood pressure and arm circumference. Methods: Seventy, 11-year-old children were studied. The Korotkoff sounds were recorded from the bell of a stethoscope to a MiniDisc system and each sound described twice on separate occasions as phase I, II, III or IV, with phase V meaning disappearance of the sound. Results: Phases I, II, III, IV and V were present in 97% (68/70), 61% (43/70), 51% (36/70), 88% (62/70) and 80% (56/70) respectively. When the recordings were blindly re-assessed there was no significant difference in the phase distribution of the sounds. All five phases were present in 40% (28/70). Phase III only occurred in the presence of phase II (P < 0.0001). There was no significant relationship between the presence of the different phases and heart rate or blood pressure. Arm circumference was significantly larger in children with phase V present (P < 0.02). Conclusions: The Korotkoff sounds and phase distribution present in normal children is described. Korotkoff sounds were consistently allocated to the various Korotkoff phases. This study provides insights into the problems of accurate diastolic blood pressure measurement. Phase V was more likely to be present with increasing arm circumference, but the variation in the occurrence of phases II and III remains unexplained.