Varicella (chickenpox) is sometimes associated with serious complications characterized bp changeable frequency in different ages. We describe a case of varicella with contemporary presence of several complications: serious impetigo , conjunctivitis, pneumonia, hepato-encephalic disease (probable Reye syndrome). This case is interesting because after adequate rehydration and normalization of electrolytes we registered a remarkable fall of plasmatic sodium and chloride as a result of hemodilution probably due to a syndrome of inappropriate secretion of antidiuretic hormone, confirmed by values of plasmatic and urinary osmolarity and of urinary electrolytes.