Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction. Clinical symptoms are caused by weakness and increased fatigability of various muscle groups. Myasthenia may lead to significant respiratory dysfunction. The aim of our study was to estimate lung function in children with MG. We tested 23 non-smoking patients (18 girls and 5 boys) aged 7-18 years. Whole-body plethysmography and spirometry were performed in all patients. In 33% of the patients a decrease in VC <80% of predicted value was observed (VC = 89 +/-19%), but the analysis of TLC revealed restrictive pattern only in one patient (TLC = 102 +/-17%). In more than 75% of the children the value of RV above 120% of predicted value was found (RV = 146 +/-54%). Spirometric obstructive pattern measured by FEV1%VC <70% was not observed, although in 56% of the patients airway resistance was increased (Raw = 132 +/-44%). In 45% of the patients a decrease of PEF (76 +/-14%) was observed. In MG children true restrictive pulmonary impairment is rarely observed and a decrease in VC in these patents seems to result mainly from functional restriction provoked by an increase in RV. Spirometry is not an optimum method to assess functional changes in MG patients. The assessment of additional measures such as TLC, RV, and Raw is desirable.