Letters to the editor published in theLancet during the first half of 1980 were less cited than the corresponding papers. The average number of citations per letter was larger if the letter contained some substantive information. The longer the letter the more frequently it was cited. Letters that react to some previous publication tend to be shorter than spontaneous letters. Reacting letters tend to be less cited than spontaneous letters if they are short, more cited if they are longer. Letters with substantive information tend to originate outside the UK in which case they are also more cited.