Ceratothripoides claratris Shumsher is one of the most important thrips pest of tomatoes in central Thailand. Hence we conducted studies to determine the intra- and inter-plant distribution of C. claratris on tomatoes in two types of greenhouses, i.e., open-plastic and closed net house. The experiments were conducted on the campus of the Asian Institute of Technology in Bangkok, Thailand. Both adults and larvae of C. claratris showed foliage-biased distribution. Sex ratios of adult C. claratris did not significantly differ on flowers and leaves, whereas on fruits males significantly outnumbered females. On flowers, no diurnal periodicity of occurrence of C. claratris was detected. Generally, thrips infestation commenced in the lower parts of the tomato plants and gradually spread to the higher strata of the plants. Depending on the greenhouse type and the stem system thrips infestation differed significantly over time in the lower but not in the uppermost strata of the plants. In the net house, infestations of C. claratris commenced one week after planting of the tomato seedlings. Soon after the peak in infestations, thrips numbers dramatically decreased. Estimates of Taylor’s power showed that C. claratris had an aggregated distribution pattern on the foliage of tomato plants. The importance of these findings for future monitoring programs of C. claratris infestations on tomatoes is discussed.