This is the first study on the phenomenon of peer aggression or in the city of Cali, Colombia. A survey of 2,542 students of 6th, 7th and 8th grade in 14 middle- and high-schools in the city was carried out with the purpose of identifying the presence or absence of this problem, and in case it existed, of establishing the specific forms of its manifestation, discriminating by age, gender and SES. Results showed that bullying occurs in 24.7% of all students in the survey, expressed as verbal, physical or psychological aggression or intimidation in both genders and all SES's. It was also found that the most frequent form of aggression is verbal, and that this form also happens in the presence of peers and teachers in classrooms.