Contrast-induced nephropathy (CIN) is an important complication of coronary angiography (CAG) and percutaneous coronary intervention (PCI). The aim of this study was to examine the effect of CAG and PCI to renal function in patients with a low risk of CIN by measuring serum cystatin C concentration. The patients were classified into 3 groups; CAG group, elective PCI group, and emergency PCI group. Enrolment continued until 100 patients were included in each of the 3 groups. The exclusion criteria were as follows; (1) serum creatinine concentration >1.5 mg/dL, (2) age >80 years, (3) cardiogenic shock, (4) use of mechanical ventilation or intra-aortic balloon pump, (5) history of renal failure, and (6) quantity of contrast used > maximum radiographic contrast dose. Blood samples for serum cystatin C analysis were collected before and 3 months after the index procedure. Two patients in the CAG group, 4 patients in the elective PCI group, and 12 patients in the emergency PCI group developed CIN. Multivariate analysis identified the predictors of CIN: pre-procedural cystatin C concentration >1.04 mg/L, contrast volume >150 mL and emergency procedure. In the elective PCI group and emergency PCI group, serum cystatin C concentration was significantly increased 3 months after PCI procedure. Even patients with a low risk of CIN developed CIN after CAG and PCI, which caused increase of serum cystatin C concentration. We should become more aware of the possible development of CIN and avoid performing unnecessary CAG and PCI procedure as far as possible.