It is important to start treatment from an early stage of IgA nephropathy although there is still no specific treatment at present. Surveillance of long-term 5-year treatment with dilazep hydrochloride (Comerian), an anti-platelet drug, in 106 patients with IgA nephropathy was conducted at 52 clinical sites in the Tokyo area of Japan. Results obtained in the present study were as follows: 1) 106 patients who received dilazep hydrochloride for 5 years or lomger were either in the relatively good prognosis group or in the relatively poor prognosis group. 2) Urinary protein excretion was decreased: 35.1% of the patients were considered “improved” and 54.5% were “slightly improved or better”. 3) Creatinine clearance (CCr) was not significantly changed with a low improvement rate: 3.5% of the patients were considered “improved” and 10.5% were “slightly improved or better”, but fewer patients were judged “aggravated”(17.5%). 4) Favorable improvement effects on erythrocytes in urine were observed: 22.6% of the patients were considered “improved” and 50.0% were “slightly improved or better”. 5) Leukocytes increased as an adverse drug reaction in one patient (0.9%). These results showed that dilazep hydrocholide is safe and well tolerated in long-term treatment, and has a beneficial effect on several urinary findings, indicating that it is effective in maintaining renal function. Therefore, dilazep hydrochloride can be considered as the first line drug for patients with IgA nephropathy, in whom only relatively-mild tissue damage and comparatively stable progress are observed.