Brachylaima cribbi is a terrestrial trematode parasite of humans and other mammals, birds and reptiles, with helicid and hygromiid summer-aestivating land snails acting as first and second intermediate hosts. Beginning in April, seasonal variations in rates of sporocyst and metacercarial infection by B. cribbi were studied in Cochlicella acuta, Cernuella virgata and Theba pisana over 1 year at four ecologically diverse sites on the Yorke Peninsula, South Australia. The overall mean sporocyst prevalence rate in April was 2.7%. Sporocyst prevalences peaked during spring (10–78% for C. acuta, 12–44% for C. virgata and 10–18% for T. pisana). Metacercarial infection rates varied markedly from 10% to 98% at the start of the study. Overall metacercarial infection rates peaked with winter rains for T. pisana (average 50% infected) and in spring for C. acuta and C. virgata (average 80% infected) then declined in summer for all species. The average numbers of metacercariae per infected snail over the study period were 5.4 for C. virgata, 3.9 for C. acuta and 2.2 for T. pisana, with maximum numbers in winter or spring. Conditions on the Yorke Peninsula favour hyperinfection with this parasite.