Dr Callejas is an assistant professor in the Department of Otolaryngology at Pontificia Universidad Católica de Chile. He completed his residency in otolaryngology at Pontificia Universidad Católica de Chile and then a fellowship in rhinology and skull base surgery with Dr. Richard Douglas in Auckland, New Zealand. He also spent 3 months of visiting observership with Professor Peter-John Wormald in Adelaide, Australia.
His current practice is divided between tertiary rhinology and endoscopic skull base surgery. He is a reviewer for several otolaryngology journals and has been co-director and director of the Advanced Endoscopic Sinus Surgery Course held biennially in Santiago, Chile. He organized the first Workshop in Endoscopic Management of Vascular Injuries in South America held in Santiago, Chile in 2016.