The risk of infection with Campylobacter jejuni/coli as well as complications may be related to host genetics. We assessed six single-nucleotide polymorphisms in inflammatory cytokine genes in 105 patients with Campylobacter jejuni/coli gastroenteritis. The population distribution of the genes was determined in healthy subjects. The patients responded to mailed questionnaires with regard to reactive arthritis (RA) and irritable bowel syndrome (IBS) in 6-month follow-up. The genotype INFG(+ 874A/A) was less frequent in patients than in controls (20% versus 33%; P = 0.015), whereas the distribution of the other five SNPs did not differ from controls. After 6 months, RA had developed in 15 subjects and IBS in 20 subjects. RA was significant more frequent in patients with IL-18(-137G/G) (22%) than IL-18(-137C/C) (0%), P = 0.03, with INFG(+874 T/T (32%) than INFG(+874A/A) (0%), P = 0.007, and with INFG(+2197 A/A) (22%) than INFG(+2197G/G) (0%), P = 0.02. The development of IBS was not linked to gene polymorphisms. In conclusion, the risk of acquiring clinical gastroenteritis with Campylobacter jejuni/coli is related to the INFG (+ 874A>T) of intron 1. Polymorphisms in IL-18 and INFG are linked to the risk of post-infectious reactive arthritis, but not to irritable bowel syndrome.