Oral candidiasis is a common oral caused by overgrowth of fungal species in the genus Candida. These microorganisms reside in the oral cavity as a part of normal microflora, but can cause disease when the host is predisposed. Several local and systemic host factors, particularly impaired immunity, can facilitate opportunistic infection by Candida species. Therefore, the rising number of population with immunocompromising conditions including HIV infection, old age, malignancies and other critical illnesses-may have led to the gradual increase in the prevalence of oral candidiasis over the past decade. Clinical manifestations of oralcandidiasis can vary considerably, and may pose difficulties in clinical diagnosis in certain cases. These lesions may cause burning sensation and interfere with food intake, thus adversely affect the patients' general health and quality of life. Furthermore, oral candidiasis reflects problems in underlying health status, which may not have previously been recagnized. Therefore, dentists play an important role in the diagnosis, treatment, and health maintenance of and increasing number of patients at risk. To achieve therapeutic success, dentists need to recognize the importance of determining host factors contributing to the infection so that they can be corrected simultaneously with antifungal treatment. In Part 1, the artical discusses the various clinacal manifestations of oral candidiasis and its etiology with respect to both the host's predisposing factors and the causative microorganisms and their virulence factors. Current guidelines for the treatment and prophylaxis of oral candidiasis will be discussed in the following Part 2 article.