Body movements (BMs) during night sleep of 25 neurologically normal infants, 11 premature and 14 full-term, whose ages ranged from 30 conceptional weeks to 18 months post-term, were examined to evaluate the changes of their features with age. The examinations performed during sleep periods totaled 65 times, 1 to 60 times on each subject. Through visual observation and EEG recordings, the BMs were classified into 3 types: (1) Gross movements (GM), (2) localized movements (LM), both of the above two lasting more than 0.5 second, and (3) twitch movements (TM) lasting less than 0.5 second. Total GM and LM time per hour of sleep, average duration of GM and LM and number of GM, LM and TM per hour of sleep were calculated. Percentage of 20 seconds epochs without BMs (nonbody-movement-epochs) was also estimated. These BMs parameters decreased with maturation to certain low base levels. However, each parameter showed a particular time course. TM decreased initially, then LM and lastly GM reached the base level around the age of 9 to 13 months. On the other hand, nonbody movement-epochs increased progressively until 8 months of age. These three types of BMs are considered to be controlled by the CNS with different organization levels, the simplest for TM and the most complicated for GM. They are thus correlated to the maturational process of the CNS, and could be good indicators for detecting normal and abnormal CNS developments.