Purpose <p>To report a rare case of bilateral idiopathic multifocal retinal pigment epithelial detachments (imfPEDs) and to describe the long-term morphological and functional changes observed over a 16-year follow-up period.</p> Methods <p>A 49-year-old woman was diagnosed with imfPEDs based on multimodal imaging, including optical coherence tomography (OCT), fluorescein angiography (FA), and fundus photography. Full-field electroretinograms (ffERGs) and multifocal ERGs (mfERGs) were recorded to assess retinal function. The patient voluntarily discontinued follow-up but returned 16 years later due to cataract progression. Retinal morphology and function were re-evaluated using comparable multimodal imaging and electrophysiological methods.</p> Results <p>At the initial visit, multiple bilateral pigment epithelial detachments (PEDs) were identified. OCT showed hyporeflective, dome-shaped PEDs with smooth borders, and ERG responses were within normal limits. Sixteen years later, some PEDs had resolved, others had newly developed or fused, and geographic atrophy was observed, particularly in the peripheral retina. Fundus autofluorescence (FAF), performed in place of FA, revealed hyperautofluorescent PEDs and numerous peripheral hypofluorescent spots. ffERGs remained normal, while mfERGs showed localized attenuation with relatively preserved macular function. These findings were consistent with large colloid drusen and cuticular drusen.</p> Conclusion <p>This case demonstrates the slow morphological progression and relative functional preservation in bilateral imfPEDs over 16 years. Comparable multimodal imaging and electrophysiological testing were valuable in monitoring the long-term clinical course and support the classification of this phenotype as a variant of large colloid or cuticular drusen.</p>