AIMS: To alert pathologists to the spectrum of histological appearances that may be seen in injection site reactions related to aluminium. METHODS: Four cases of injection site reaction were examined microscopically using routine staining with haematoxylin and eosin, electron microscopy and by electron probe microanalysis. RESULTS: As in previous reports, all four cases included collections of histiocytes which contained faint granular brownish refractile material within their cytoplasm; ultrastructural examination showed this to be aluminium. Two cases showed a prominent inflammatory reaction with numerous lymphoid follicles and a notable eosinophilic infiltrate. Two cases showed unusual features not described previously. In one, there was a sclerosing lipogranuloma-like reaction with unlined cystic spaces containing crystalline material. The other case presented as a large symptomatic subcutaneous swelling which microscopically showed diffuse and wide-spread involvement of the subcutis by a lymphoid infiltrate with prominent lymphoid follicles. CONCLUSIONS: This report highlights the changes encountered in aluminium injection site reactions and emphasises that the lesions have a wider range of histological appearances than described previously.