A field evaluation of a new area repellent system, Thermacell Mosquito Repellent (TMR, cis-trans allethrin), was conducted against phlebotomine sand flies and mosquitoes in Cunpolat village, Sanlıurfa Province, in southeastern Anatolia, Turkey, an area historically endemic for cutaneous leishmaniasis and high sand fly populations. The objective of this study was to determine the efficacy, duration of protection, and spatial characteristics of protection (downwind distance from point of release), of the TMR. Twelve adult volunteers (nine in the treatment and three controls) made collections from ankle to knee for 25 min every hour from 2100 to 0300 on six consecutive nights in August 2002. Treatment consisted of placing a TMR unit at the middle of the village and then placing human bait collectors at 2.3, 4.6, and 7.6 m away from the repellent unit. Results from the field tests showed highly significant protection provided by the TMR from attack by Phlebotomus papatasi (Scopoli) (P < 0.001) and Ochlerotatus caspius (Pallas) (P < 0.001) for up to 4 h postapplication. In the six nights that tests were done, a total of 949 sand flies and 1095 mosquitoes were collected from the untreated control sites. Only 86 sand flies and 83 mosquitoes were collected at all distances from the places treated with TMR. These results indicated that reduction in sand fly and mosquito biting rates in treated groups ranged from 87.5 to 97.7% (mean protection 92%) and 90.2–97.4% (mean protection 93%), respectively. The percentage reduction values were maintained above 90.0% for 6 h of the assessment period. Overall, the number of bites by the cutaneous leishmaniasis vector Ph. papatasi and also Oc. caspius was reduced >11-fold and 13-fold, respectively, by the TMR.