The authors report on five cases of Seckel syndrome type I primordial dwarfism, belonging to three unrelated sibships. Immunological and cytogenetic investigations with DEB test did not evidence immunodeficiency or chromosomal fragility. HLA phenotype studies revealed an identical haplotype in affected sibs: a possible linkage with HLA is therefore suggested. Cranial magnetic resonance was performed in three patients and did not evidence any anomaly. One affected female showed precocious puberty at 7 years of age.