Background. Fungal infection represents a growing problem in children with hematologic malignancies. During chemotherapy induced neutropenia, colonization with fungi is considered a major risk factor for subsequent fungal infection. The rates and risk factors for mycotic infections in pediatric oncology patients is undetermined, particularly for centers in developing countries. The aim of this study was to evaluate the rates and risk factors of fungal colonization in children with acute leukemia and lymphoma at one of the major pediatric hematology/oncology centers in Turkey. Procedure. Fifty-two consecutive children newly di- agnosed with acute leukemia and lymphoma during intensive remission induction therapy were evaluated for the occurrence of fungal colonization (defined as at least one positive surveillance culture) and infection. Results. Thirty-six of the 52 patients (69.2%) were colonized by Candida albicans which was the only fungus isolated from surveillance cultures. There were three (5.8%) proven systemic fungal infections: two cases of candidemia and one case of brain abscess with Aspergillus spp. isolated from tissue. All patients with fungal colonization were receiving prophylactic or curative antibiotics. No significant association was found between type of disease and fungal colonization, but there was a significant association with neutropenia. Conclusions. Our findings suggest that there is a high rate of fungal colonization in children receiving remission induction therapy for acute leukemia and lymphoma. Limiting the use of antibiotics and instituting antifungal chemoprophylaxis may decrease the rate, while the early initiation of empiric antifungal therapy in patients with fever and suspected mycotic colonization may increase survival in these patients. Med. Pediatr. Oncol. 32: 344-348, 1999.