Abstract Nocardia and Actinomyces are Gram-positive bacteria of the order Actinomycetales. These ubiquitous organisms exhibit filamentous branching structures, which sometimes coalesce and develop into bundles known as mycelia. They are the cause of rare, but clinically important, infections and are often termed ‘the great masqueraders'. Affected individuals tend to present with chronic debilitating suppurative infections, and there can be a significant delay before a definitive diagnosis is made. Microbiological diagnosis is challenging, but advances in molecular techniques are improving the identification of these organisms. Despite the relative rarity of these conditions, an awareness of the disease manifestations caused by these organisms is beneficial; outcomes are more favourable if they are diagnosed early and effective treatment is initiated.