Abstract Biologic therapies have revolutionised disease control in patients with rheumatoid arthritis (RA). Theoretically, they have the potential to influence co-morbid disease associated with RA through better control of systemic inflammation. Conversely, co-morbidity may occur as an adverse effect of the drugs. The latest evidence from observational data shows an increased risk of infection in the first 6 months of treatment with tumour necrosis factor inhibitor (TNFi) therapies and potentially other biologic therapies. Rates of infection after the first 6 months decrease and become comparable to patients with RA treated with conventional synthetic disease modifying anti-rheumatic drugs (csDMARDs). TNFi also appear to reduce the risk of cardiovascular disease in these patients, in particular ischaemic heart disease. TNFi treatment may be associated with a small increase in the risk of developing squamous cell carcinoma of the skin; in terms of other cancers, rates appears to be no different to those seen in patients treated with csDMARDs. There is a paucity of data on the impact of other biologic therapies and the effect of all biologic therapies on other common co-morbidities.