Thiomersal keratoconjunctivitis is a common problem in soft contact lens wearers, accounting for thirty two (10%) of three hundred and twelve consecutive referrals for contact lens related problems to an out patient department. The clinical findings in 55 patients are described, of which 42 show the 'typical' appearance of the condition. This consists of non-specific conjunctival changes, limbal follicles, superficial punctate keratopathy and superior corneal epithelial opacity. Thirteen atypical cases are presented, demonstrating superior limbitis occurring in isolation, coarse punctate keratopathy, severe keratopathy with visual loss, pseudo-dendritic corneal lesions, acute conjunctival hyperaemia without keratopathy. Symptoms were also seen in two patients who were hard lens wearers. In such atypical cases, diagnosis may be difficult but can be aided by the use of topical challenge with thiomersal.