The study aimed to assess rates of illegal cigarette sales to children and the impact on these rates of publicity and a warning letter threatening prosecution. Children aged 12 and 13 made two repeat purchasing attempts, three months apart, at 255 randomly selected tobacco retail outlets in Sydney. A randomly selected 50 per cent of retail outlets which sold cigarettes illegally at the first attempt were sent warning letters threatening prosecution. Publicity about the undercover buying operation was organised between the attempts. At the first attempts, 39 per cent of shops sold cigarettes to the children and 32 per cent sold them at the second attempt. Shops which sold on the first occasion and received warning letters reduced selling by 69 per cent compared to the 40 per cent reduction in shops which sold cigarettes on the first attempt and were not sent warning letters, a net reduction of 29 per cent seemingly attributable to the warning letters (95 per cent confidence interval 8 per cent to 50 per cent). It is extremely easy for children as young as 12 to buy cigarettes. The combined effects of publicity about undercover buying operations and warning letters threatening prosecution seem capable of reducing selling by about 29 per cent. Because of inconsistencies in selling or refusals, future attempts to measure selling rates to children should use repeat purchasing attempts and classify outlets as 'selling', 'not selling' or 'sometimes selling'.