The annual numbers of cases of non-tuberculous mycobacterial lymphadenitis in south east England has increased over the period 1973 to 1993, most notably during the last few years. The most frequent cause is the Mycobacterium avium complex, followed by M malmoense. The reason for the increase is unknown but it could be due to an increased awareness in mycobacterial disease, an external factor such as pollution, or both.