The use of in situ hybridization to detect and characterize chromosome anomalies on cytogenetic preparations is now largely applied in clinical laboratories. Its use in embryofetopathology on formalin-fixed and paraffin-embedded tissues, when an aneuploid condition is suspected but a routine chromosomal analysis is not possible was assessed in the present study. Control values of hybridization signals obtained after different enzymatic digestion protocols have been established on normal fetal tissues. Tissue conservation and fetal age as well as other parameters have also been analysed. A successful hybridization has been achieved in most cases. Failure of hybridization was observed in specimens associated with extensive tissular lysis. In conclusion, the application of in situ hybridization on fetal tissues is very useful to detect chromosome anomalies in embryofetopathology.