PURPOSE: Concern about the survival of microorganisms in deep carious lesions may often lead to unnecessary exposure of the pulp during excavation. This study evaluated the relationship between microbiological and clinical results of deep carious lesions in primary molars. METHODS: Clinical evaluation was performed on 72 deep carious lesions considered to have pulp perforation after traditional excavation. The dentin color and consistency were assessed by means of standardized scales using the technique of Bjorndal et al before restoration. For microbiological examination, dentin samples were taken by a sterile bur and transferred to transport fluid, then plated on tryptic soy agar for growth of total colony forming units. Samples werethen transferred on Rogosa SL agar for growth of oral lactobacilli and on mitis salivarius agar for growth of mutans streptococci. RESULTS: The proportion of mutans streptococci, lactobacilli, and total colony forming units increased when the dentin color and consistency increased. However, the proportion of lactobacilli was smaller than that of mutans streptococci in carious dentin samples. CONCLUSIONS: Contrary to expectations, the findings showed that the number of bacteria in carious dentin of primary molars was not significantly excessive.