Using a multilevel random-coefficient approach, we examined the longitudinal association between toddlers' early shyness and their well-being during their first year in Norwegian early childhood education and care (ECEC) centres. We used data from two measurement points (preintervention and postintervention) from a larger cluster randomized controlled trial study, Thrive by 3. We followed 567 children (answered by 415 mothers and 152 fathers) who were younger than 19 months and had just started in ECEC at preintervention. Our findings indicate that toddlers' early shyness during their starting period in ECEC is associated with their well-being by the end of their first year in ECEC. Our findings highlight the importance of paying extra attention to shy toddlers, as they seem to show less well-being during their early period in ECEC.