The risks of precipitating acute angle-closure glaucoma is always present when eyes have shallow anterior chambers, and early recognition of angle-closure glaucoma is important to prevent permanent loss of vision. Two groups of patients with acute angle-closure glaucoma are presented: in the first the attack was immediately preceded by the use of a mydriatic agent and in the second a mydriatic agent had been used previously without incident but the patient later presented with a spontaneous acute attack. A shallow anterior chamber, and in particular inequality of anterior chamber depths of greater than 0.2 mm, were important indicators of susceptibility to angle closure, which is more common in women than in men. Where there is a risk of angle closure, tropicamide 0.5% appears to be the safest mydriatic agent and should be followed by the administration of a miotic agent in susceptible individuals. The need to carry out a peripheral iridectomy in the other eye is stressed, irrespective of the age of the patient. A case of acute glaucoma after the use of oral drops that contained belladonna for nasal allergy further highlights the risks of the use of systemic mydriatic agents in susceptible individuals.