Abstract To determine the microbiological agents in conjunctivitis in children and young adults, physicians outside hospitals were asked to obtain samples from the conjunctiva in patients presenting with conjunctivitis. Specimens from 194 patients and 177 healthy controls were cultivated for Chlamydia trachomatis. In 12 cases Chlamydia trachomatis was isolated (i.e. 4 neonates, 1 three-year-old child and 7 adults, aged 17 to 39 years), but in none of the controls. Of the specimens from patients 168 and all of the healthy controls were cultivated for both bacteria (including Chlamydia trachomatis) and viruses. The main microorganisms, regarded as infectious, were Haemophilus influenzae (20), Streptococcus pneumoniae (18), Staphylococcus aureus (14) and Chlamydia trachomatis (9). Haemophilus influenzae (non-typable strains) were isolated more frequently in the age group below 5 years of age than in the age group 5–50 years. Herpes simplex virus (type II) was isolated in one neonate. Chlamydia trachomatis is among the most important infectious agents in conjunctivitis treated outside hospitals. As chlamydial infections need special attention regarding treatment and follow-up, physicians should be encouraged to obtain specimens for microbiological examination, including chlamydia, from the population at risk.