OBJECTIVE: In early infancy the infant's thumb is not infrequently enclosed within the palm, ie, thumb-in-fist (TIF). This posture has received scant attention in the neurodevelopmental literature. Its prevalence, resolution, and clinical associations were investigated in this study. METHODOLOGY: Two hundred sequentially born, apparently healthy full-term newborn infants comprised the cohort. The whole study group was followed up until the disappearance of the TIF occurred. In the first 150 of the cohort, additional data on development and the neurological status were obtained at 12 months of life. RESULTS: In 125 infants (62.5%) of the total cohort, a TIF was noted. The mean age of disappearance was 1.5 months, and no TIF persisted after 7 months old. No relationship was noted between the TIF resolution and abnormal neurological signs or gross or fine motor development. The only association noted between age of resolution of the TIF and the neurodevelopmental status was a delay in language attainment at the 12-month screening. CONCLUSIONS: The TIF posture in infancy was noted in 65% of our cohort, and it had resolved in all infants by 7 months old. Therefore, a TIF posture after this age should alert the clinician to the possibility of possible neurological dysfunction. An unanticipated association of a delay in the 12-month language milestone attainment was noted in those infants with later resolution of the TIF posture. No data on language development in this group were obtained after 12 months old; therefore, the clinical significance of this finding is not yet elucidated.