The oxygen concentrator is an effective supply source in home oxygen-therapy (HO). In order to study the effectivity of the concentrator in HO, we visited at home 31 patients using the concentrator as the only oxygen supply source in the exit gas and counted the hours of concentrator usage. Only 13 concentrators (41.9%) supplied a percentage of oxygen higher than 87% at a flow of two liters per minute. In three cases (9.7%), sporadic control measures of the percentage of oxygen in the exit gas were being taken and only four patients (12.9%) said that these controls were made monthly. The concentrator did not supply the adequate percentage of oxygen in 12 out of the 29 patients correctly taking the HO, so the effectivity of the treatment can only be expected in 28.6% of studied cases. The concentrator operates well under ideal conditions, but potential breakdowns in standard conditions of use must be considered. The efficiency of the HO with concentrator in our environment is very low, but it can be improved with regular controls of the concentrators or the introduction of devices warning the patient when they detect a reduction of the percentage of oxygen in the exit gas.