Primary palmar hyperhidrosis is a distressing and disabling condition that can produce social, psychological and occupational problems. Although the use of botulinum toxin type A (BoNT-A) has been reported as an efficacious and safe intervention to improve palmar hyperhidrosis, only one study concerned botulinum toxin type B (BoNT-B) in this disorder. The aim of study was to evaluate the efficacy and safety of BoNT-B in treating primary palmar hyperhidrosis. Participants were injected with 5,000 IU of BoNT-B in each palm. Visual analogue test (VAS) to evaluate the intensity of decrease in sweat production, Minor's iodine starch test and measurement of paper towels' weight were used to ascertain palmar sweating at baseline, 4, 12 and 24 weeks after BoNT-B injections by a blind examiner. Thirty-two subjects (12 males, 20 females, mean age 31 ± 11) were enrolled. Significant reduction of palmar sweating was detected after BoNT-B injection: 2.9 ± 1.4, 0.3 ± 0.4, 0.9 ± 0.8, and 2.1 ± 1.5 g (p < 0.001) of paper towels' weight for the right palm at baseline, 4, 12 and 24 weeks; and 2.8 ± 1.7, 0.5 ± 0.6, 0.8 ± 0.7, and 1.8 ± 1.25 g (p < 0.001) at same time, respectively for the left palm. Significant reduction of mean VAS values were also detected after BoNT-B injections: 8.6 ± 1.1, 0.6 ± 0.8, 3.5 ± 2.5, and 7.1 ± 2.4 (p < 0.0001) at baseline, 4, 12 and 24 weeks, respectively. Mild side effects consisting in local pain and hand weakness were observed in 4 (12.5%) subjects. The findings indicated that the use of 5,000 IU BoNT-B injection in each palm was safe and significantly improved the severity of palmar hyperhidrosis.