During long-term follow-up of the patients with obstructive sleep apnea syndrome (OSAS) under the positive airway pressure (PAP) therapy, it waits to be explored whether or when routine retitrations are indicated. We prospectively followed up 133 patients for 10 years to define which demographical or polysomnographic factors should be taken into account to determine the need for retitration. Patients were retitrated at 1st, 2nd, 5th, and 10th follow-up years. A change in pressures >= 2cmH(2)O was present in more than half of the patients at 2nd and 5th years. Changes in weight for at least 10 kg showed a significant correlation with the changes in pressures >= 2cmH(2)O (p = 0.023) and >= 3cmH(2)O (p = 0.047) at 2nd year. OSAS-related complaints, nasal or upper airway surgery, or emergence of cardiovascular diseases were not correlated with the changes in pressures. Apnea-hypopnea index (AHI) at diagnostic night was positively correlated with the changes in pressures >= 3cmH(2)O at 1st and 5th years. The percentage of N3 sleep at first titration night showed positive correlation with changes in pressures >= 3cmH(2)O at 2nd and 5th years. The index of periodic leg movements in sleep (PLMS) and PLMS-arousal index at first titration night was positively correlated with any change in pressures at 2nd and 5th years. Our findings showed that vast changes in weight, high AHI at diagnostic night, increased duration of deep NREM sleep and high PLMS and PLMS-arousal indices at first titration night should be noted as important indicators for retitration within the first 5 years of follow-up.