Calcium pyrophosphate dehydrate (CPPD) crystal deposition disease (also known as chondrocalcinosis, CC) is a rare metabolic arthropathy mostly seen in elderly patients. Chondrocalcinosis may be associated with metabolic diseases such as hypomagnesemia when it occurs in young people. We report here a case with hypomagnesemia due to familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) who developed CC during clinical follow-up. To our best knowledge this is the first case of a young patient with CPPD associated with FHHNC.