Background: Little is known about sensitization to iron (Fe) in private, occupational, and medical settings, particulary implantology.Objectives: To investigate sensitization to metals, particularly to Fe, both in preimplant individuals with presumed metal allergy and in patients with suspected metal implant allergy. To further characterize Fe-sensitized individuals.Methods: Analysis of patch test reactions to an Fe (II) sulfate-containing metal series in 183 consecutive patients (41 pre-implant, 142 metal implant bearers). Test readings were on day (D)2, D3, and D6. Evaluation of questionnaire-aided history of metal reactivity patterns and demographics of Fe reactors.Results: Metal reactivity in pre-implant/implant/total group was: to nickel 39%/30%/32%; to cobalt 17%/15%/15%; and to chromium 7%/13%/11%.Co-sensitizations cobalt/nickel (19/58) and cobalt/chromium (11/21) were significant at P < .001; co-sensitizations Fe/nickel (4/10) and chromium/knee arthroplasty (11/73) at P = .03. Ten of 183 (5.5%) reacted to Fe (2 of 41 pre-implant patients, 8 of 142 implant bearers), with 10 reacting only on D6. Fe reactivity was highest in complicated knee arthroplasty (7/73). Further peculiarities of Fe reactors included frequent isolated Fe reactivity (6/10), occupational metal exposure (7/10), previous (par)enteral Fe substitution (6/10).Conclusions: The 5.5% prevalence of Fe reactions suggests a potentially underestimated role of this metal allergen in general and in implant bearers. The latter also shows a distinct metal sensitization pattern.