to determine frequency, serotypes, biotypes and susceptibility to eight antibiotics in Haemophilus influenzae nasopharyngeal isolates in children under five years old from Mexico City. cross-sectional survey including children two months to five years old. A nasopharyngeal sample was taken. Haemophilus influenzae identification, serotyping, biotyping and antimicrobial susceptibility were performed. a sample of 573 children were included. In 88/573 (15.3 %) H. influenzae was isolated, corresponding in 7/573 (1.2 %) to Hib, 3/573 (0.5 %) to Hi a, c, d, f and 78/573 (13.6 %) to Nontypable Hi. Among Hib carriers, 6 had received only one or two doses of specific vaccine. Biotype VIII (76.1 %) was the predominant. All isolates were susceptible to the antibiotics, but one Hib strain was resistant to erithromycin. nontypable Haemophilus influenzae was predominant. Colonization by Hib in children under 5 years old was low (1.2 %), occurring in children with an incomplete vaccination schedule.