INTRODUCTION: Idiopathic normal pressure hydrocephalus (iNPH), a condition that primarily affects the elderly, has an unclear prevalence rate in China. METHODS: A cross-sectional survey involving 1491 seniors aged 60 and above in Shanghai was conducted. Clinical symptoms and brain imaging data were collected for the diagnosis of suboptimal probable iNPH (s-probable iNPH). The crude prevalence was calculated and the estimated prevalence was inferred. RESULTS: The crude prevalence of s-probable iNPH was 3.09% and 2.62% respectively, using DESH score ≥6 and Radscale score ≥7 as the primary imaging diagnostic criteria. The estimated prevalence of Shanghai was 2.59% among people over 60 years old and it rose to 7.99% among people aged over 90, and it was estimated that 134,152 and 11,708, respectively, had s-probable iNPH among the corresponding age group. DISCUSSION: The prevalence of s-probable iNPH fluctuates based on the radiological scoring systems and the defined thresholds employed, and it tends to rise with advancing age.