This first survey of the ant fauna in a children's hospital in the city of Palmas, state of Tocantins, compares species composition, abundance and infestation rate of ants between rainy and dry seasons, day and night periods, and among 15 hospital sectors. Forty-eight collections, being 12 diurnal and 12 nocturnal in each season using five attractive baits distributed per sector, maintained for 3h per sampling. A total of 34,309 ants were collected, distributed in 12 species: Acromyrmex sp., Brachymyrmex sp., Camponotus spp. (four morphospecies), Dorymyrmex sp., Tetramorium sp., Solenopsis globularia (Creighton), Solenopsis saevissima Smith, Tapinoma melanocephalum (Fabricius) and Paratrechina longicornis (Latreille). The hospital presented an average building infestation rate (40.3%), when compared with hospitals from other Brazilian regions. In general, there was no difference in the species composition between seasons and the period of the day, although abundance of ants was higher at night. The dry season and the nocturnal period showed the highest infestation rate, mainly by T.melanocephalum and S.globularia. Gynecologic ward, lactation unit, preconception and pediatric ward access ramp showed higher infestation rate, although these varied between seasons. The significant infestation levels by the three species above, especially in sectors with restricted access such as lactation unit, laboratory, Intensive Care Unit e surgery center, indicate potential risks for contamination of patients by multi resistant pathogens possibly present in ants' bodies, as verified in others studies.