Cryptosporidiosis is one of the most common causes of diarrhoea worldwide, especially in the vulnerable groups of children between 0-5 years and immunocompromised individuals. The purpose of the study is to estimate the prevalence of the Cryptosporidium infectionin children from North-eastern Bulgaria and to determine the specifics of the clinical forms through the detailed description of several clinical cases. Material/Methods: Stool samples of 458 children were investigated for the presence of Cryptosporidium spp. oocysts with specialized modified Ziehl–Neelsen staining and with an immunological test for detection of stool antigens. Prevalence estimates are presented in four groups -aged less than five years with or without symptoms and more than five with or without symptoms. Results: The overall prevalence of cryptosporidiosis in children from North-eastern Bulgaria is 2.18% with the highest incidence (3.06%) in the age group between 0-5 years with diarrhoea. All different types of infestation of the gastrointestinal tract are observed, from an acute infection that requires hospitalization, through mild or persistent diarrhoea and asymptomatic invasion (in1.53%). For each of the specified forms, the details of the clinical presentation, laboratory and physical findings are presented as separate clinical cases. Conclusions: Our findings demonstrate that broad-spectrum of clinical forms of Cryptosporidium-associated diarrhoea in children exist but up till this study are typically mis- or undiagnosed. The tendency that exists in eastern European countries, including ours, to neglect or underestimate the impact of cryptosporidiosis, is particularly dangerous and should be changed especially in the risk groups of children and immunocompetent adults.