Machine learning (ML) has proven to be a key enabler of various industrial cyber-physical systems-empowered functionalities, such as predictive maintenance (PdM) in Industry 4.0. Among many ML methods, the scope of this paper is self-organizing map (SOM). SOM has many attractive properties for industry applications (e.g., unsupervised learning, noise robustness). Further, it can yield various tasks (e.g., clustering, dimensionality reduction, health indicator construction, visualization, etc.), rendering it versatile for data-driven PdM, including anomaly detection, diagnosis, and prognosis tasks. This papers presents a brief review of the main SOM applications in the PdM field, as well as future research opportunities.