Eight hypertensive crises (HC) were treated with 2.5 mg of sublingual nifedipine in three children with weights below 10 kg (group A); 16 HC in 6 children between 10 and 20 kg with 5 mg (group B); and 40 HC in 10 children over 20 kg with 10 mg of nifedipine (group C). The relative decrease in both systolic and diastolic blood pressure was similar in all groups. The decrease was more rapid in groups A and B when the contents were extracted from the capsule and given directly. The hypotensive effect lasted 4 h. There were no side effects. The effective and safe single dose of nifedipine has been established to be 2.5 mg for children weighing less than 10 kg, and 5 mg for children weighing between 10 and 20 kg.