MEN1 and multiple endocrine neoplasia type 1: The strengths of this study involve: i) collection of the largest series of consecutive patients with hereditary PHPT having full clinical, biochemical, instrumental and genetic characterization, mostly followed at a single Italian institution; ii) inclusion of a large cohort of sporadic MEN1 cases; iii) comparison between the clinical characteristics of patients with sporadic and familial MEN1 syndrome; iv) genotype-phenotype correlation between MEN1-positive and MEN1-negative patients.