Dynamic spirometry was examined in 23 non-smoking hemiplegic patients after the acute phase. The decrease of slow inspiratory forced capacity is related to motor impairment and does not vary with time. The forced inspiratory and expiratory vital capacities are similar to the slow inspiratory vital capacity in the first 6 months of the disease, but significantly decrease later independent of the motor impairment. The peak expiratory flow is highly variable but is clearly decreased, and is related to motor impairment. These results point to a restrictive respiratory syndrome due to mechanical limitation of thorax excursions caused by weakness, hypotonicity, and incoordination of the trunk musculature. The importance of long-term physiotherapy of the trunk is emphasized.