Positional plagiocephaly has attained widespread attention. There is a lot of data on helmet therapy available, but the natural course of the deformity has not been investigated in depth. The decision for or against helmet therapy can be controversial. This study examined the outcome of both options.128 infants were enrolled in this prospective, non-randomized, longitudinal study. 62 were treated with and 66 without a helmet. The initial cranial vault asymmetry index (modified CVAI) was determined at 6.3 and 6.2 months of age (SD 1.44/2.14). Follow-up took place at the end of helmet therapy (age: 10.2 months, SD 1.77) or after 1 year (age: 18.5 months, SD 2.28) respectively. The outcome and the correlation of the changes to the initial asymmetry were compared.All infants showed a significant reduction of their plagiocephaly. Although children with helmet had more severe asymmetry initially, they showed significantly better improvement (68% vs. 31%). Only a weak correlation was found between the initial asymmetry and the amount of improvement in both groups.Despite concerns against helmet therapy (comfort, finances), it should be the treatment of choice for moderate to severe cases. Only mild cases (modified CVAI ≤ 6.5%) can be adequately treated by conservative, i.e. non-helmet, management.