The MUBICOS is a cohort of twins aiming to understand the heritability of different characteristics. The study enrolled newborn twins and multiples to follow them through childhood, aiming to study heritability, gene-environment interactions, and various neonatal and pediatric outcomes. The sample included twins who were both liveborn at least 32 weeks of gestation, and with at least one Italian-speaking parent. Since the study's inception in 2009, it has involved over 50% of the contacted families, with participation from eight birth centres, and introduced the possibility for other hospitals to join.