Mechanically-induced vasospasm often occurs during guiding catheter insertion, occasionally preventing catheter advancement to the desired location. Delicate manipulation would be impossible without the proper positioning of guiding catheters, and vasospasm-induced cerebral hypoperfusion may cause thrombotic complications. From June 2012 to December 2013, we prospectively analyzed 150 endovascular treatment cases, excluding acute cases, for the frequency of vasospasm, risk factors, and countermeasures. The associated risk factors such as the Japanese-style State-Trait Anxiety Inventory (STAI) score; anatomy and devices; and the efficacies of warm compresses, intra-arterial lidocaine/nicardipine, and tranquilizers were analyzed. Groups 1, 2, and 3 comprised 50 patients each with controls, tranquilizer administration, and prophylactic warm compresses/intra-arterial drug injection, respectively. Moderate or severe vasospasm was seen in approximately 40% patients in each group; however, severe vasospasm was absent in Group 3. Mild vasospasm-induced cerebral infarction occurred in one patient each in Groups 1 and 2. Vasospasm during diagnostic angiography [odds ratio (OR) = 10.63; P = 0.01], many ≥ 30° vessel curves [OR = 4.21; P = 0.01], and the high STAI score [OR = 1.84; P = 0.01] were risk factors for severe vasospasm. Although the relationship between anxiety and sympathetic tone remained unclear, tranquilizer administration relieved vasospasm. Warm compresses and the intra-arterial drug infusion were also useful for relieving vasospasm. Prophylactic measures such as a tranquilizer and warm compresses are expected to alleviate vasospasm; in addition, countermeasures such as the intra-arterial injection of lidocaine/nicardipine are effective.