For the vast majority of infants, the ability to sit begins around the sixth month of life. Sitting, as well as standing and crawling, are landmark milestones in gross motor development. If an infant can sit alone at around six months of age, growth and development are good. If the infant is not able to sit alone at six months of age, it is a sign of a developmental delay, and it is important to look for the appropriate cause. For example, if the infant has brain retardation, vitamin D deficiency rickets and cerebral palsy. Therefore, if the baby is normal, it can sit alone at six months after birth.