The full clinical manifestations of complications due to odontogenic foci are rarely seen in daily dental practice and can take a clinically foudroyant course of development in young people owing to anatomic conditions, as demonstrated in this clinical case in a 12-year-old girl. Endodontic treatment of the first right upper molar was started owing to increasing toothache and swelling of fossa canina and the periorbital region. During the course of treatment, the patient exhibited an acute increase in orbital inflammation, which required immediate surgical intervention with postsurgical intravenous antibiotic administration. This case should serve to emphasize the crucial requirement for intensive attention to orbital symptoms after dental procedures.