Electromagnetic Fields and Occupational Diseases. ABSTRACT. Directive 2013/35/EU, on workers’ protection from electromagnetic fields (20th individual Directive within the meaning of Article 16.1 of Directive 89/391/EEC), explicitly excludes from its purview the prevention of carcinogenic effects that may derive from electromagnetic exposure, citing a lack of conclusive evidence establishing a causal link between the two. In the meantime, the Italian Supreme Court of Cassation has taken a different approach for social security purposes, holding that causation can in fact be established between head tumours and long-term intensive exposure to electromagnetic fields given off by cell phones. This article analyzes and compares those two approaches to this new labour relations issue, which entails the allocation of liability for the negative externalities of business in connection with unknown technological risks: it looks at both the welfare side and the employer’s side (preventive measures and liability to damages for injuries). The author argues that the aforementioned EU directive appears to take an overly restrictive view of the precautionary principle set forth in the Treaty on the Functioning of the European Union. The author also discusses the systemic import of the causal-legitimacy holding reached by the Italian Supreme Court, which set a precedent not only in Italy but also in Europe and probably even in the world. This innovation in the case law seems significant not only in view of what it could mean for worker protection (as well as for consumer protection), but also because it reframes important criteria by which scientific evidence shall be assessed in court. In general, the widespread use of wireless communications can raise delicate issues in labour law, and in this regard the Italian public insurance scheme for workplace accidents can lead the way in breaking new ground on the application of the precautionary and safety-first principles. --- Relaciones Laborales is an A-ranked journal in the ANVUR classification. The Italian-language version of this article has passed the peer-review process of the journal Rivista Giuridica del Lavoro (RGL, Ediesse publishers, likewise A-ranked in the ANVUR system) and it has accordingly been revised and published in RGL, 2013, part I, pp. 737–57.