Experimental infection with Angiostrongylus vasorum was conducted in Iberian slugs Arion lusitanicus. Initially, different size/age groups of juvenile slugs (small, <0.5 g and medium, 0.5–1 g) were exposed to freshly isolated first-stage parasitic larvae (L1) of A. vasorum. The slugs were subsequently incubated at 5, 10 and 15°C for 6 weeks. Larval development within the slugs differed significantly with temperature. At 15°C, all larvae developed into the third larval stage (L3), at 10°C into the second stage (L2), whereas no development was observed at 5°C. The mean larval burdens were highest in the largest group of slugs and tended to increase with higher temperature. In a second experiment isolated L1 were incubated at 5, 10 and 15°C for 3 and 7 days prior to infection of slugs, which then were kept for 6 weeks at 15°C. The infectivity decreased significantly with the larval storage time and the mean larval burden per slug was lower at higher incubating temperature. However, all established larvae developed into infective L3. Temperature had an effect on the development of the larvae and thus an impact on transmission of the parasite as only L3 are infective to the definitive canid hosts.