Background Trunk control is generally considered to be related to gross motor development. However, this assumption has not been validated with clinical data. This pilot study was the first of its kind to examine the longitudinal development of segmental trunk control and gross motor development from 4 to 12 months of age in typically developing full-term infants. Methods A convenience cohort of 20 healthy full-term infants (mean gestation = 39.0 weeks, SD 1.2; mean birthweight = 2975.0 g, SD 297.0; males = 10) was recruited. All study infants were tested and scored monthly by independent assessors using the Segmental Assessment of Trunk Control and the Alberta Infant Motor Scale from 4 to 12 months of age. Results A developmental trend of segmental trunk control was found in the infants. Static vertical upright trunk control developed prior to active and reactive control. Statistically significant correlations were found between trunk control status and gross motor development mainly in prone and sitting positions from 8 months of age onwards (all p < 0.004, Spearman's r ranged from 0.644 to 0.798). Conclusions This pilot study provides preliminary clinical evidence to support the inter-dependency between vertical upright trunk control and gross motor development in young infants, particularly as upright functional skills are gained. This suggests that a dual focus on training upright trunk control alongside gross motor skills could be of benefit in the treatment of infants with movement disorders.