Background: Young children and rarely adolescents with cystic fibrosis can develop hyponatremic hypochloremic dehydration with metabolic alkalosis. The purpose of this article was to review the incidence of this metabolic disorder in our CF patients.Methods: We investigated the medical records of all children diagnosed with cystic fibrosis who are under follow-up in the CF center at the University Childrenʹs Hospital Ljubljana, and were hospitalised or treated on an outpatient basis due to hyponatremic, hypochloremic dehydration in the period from 2007–2012. Data analysis included clinical and laboratory findings.Results: A total of 4 children (7.2 %) from Ljubljana CF center (55 patients under the age of 19 years) were enrolled in the study. We observed 5 episodes of hyponatremic hypochloremic dehydration in 4 patients (one boy had two episodes). All were homozigous for ΔF 508 mutation. Two had episodes in summer and two in autumn, so that no season prevalence of its occurence was found. Median age at admission to the hospital due to hyponatremic hypochloremic dehydration was 7 months (range 4–34). One boy had a hypovolemic shock at the time of admission to the hospital.Conclusions: The results of our study show that dehydration with hypoelectrolytaemia is a rare complication in children with CF in Slovenia, but due to the severity of clinical signs it is an important disorder. Vomiting and fatigue are the warning signs that should alert parents and physicians to consider the possibility of this complication which can be prevented by proper hydration and salt replacement. If left untreated, it can cause seizures, arrhythmias and even death.