Objective: In our study, the morphologic structures of the jejunum and ileum sections of small intestine were investigated in human fetuses during the fetal period. Materials and methods: The study was realised on 131 human fetuses (male: 69; female: 62) with ages between 10 and 40 weeks, which have got no external pathology and anomalies. The external sizes of fetuses were measured, and then the structures in the abdominal cavity were determined by the abdominal dissection. The localization of jejunum and ileum, duodenojejunal flexure and ileal orifice points, the measurements of macroscopic diameters, types of the mass of jejunum and ileum and the localization according to the abdominal regions of the mass of jejunum and ileum were determined. Also, the samples of the jejunum and ileum were examined both macroscopically and microscopically. The thickness of tunica serosa, tunica muscularis and tunica mucosa was determined under the light microscope. Results: According to the sexes, gestastional ages and groups, the averages and the standard deviations of the all parameters were determined. The correlations between the parameters were determined. The percentage of parameters was compared according to sex and among groups. No differences were found in parameters between sexes (p < 0.05). The macroscopic parameters were increased according to the gestational age. The thickness of tunica serosa did not change according to the gestational age. Conclusion: It is thought that the data we have will help the evaluation of jejunum and ileum in intrauterine period; we also believe that the data in our study may help in the diagnosis and treatment of anomalies and pathologies in fetal period that belongs to jejunum and ileum. (C) 2003 Elsevier Ireland Ltd. All rights reserved.