Purpose. Helmet therapy is regularly prescribed in infants with positional skull deformation. Evidence on the effectiveness is lacking, which complicates decision making. This study aims to assess the relation between parents’ decision for treatment of skull deformation in their infant and their level of anxiety, decisional conflict, expectations of treatment effect, perceived severity of deformation and perceived side effects. Methods. Parents of 5-month-old infants with skull deformation were invited to participate in a survey. Data collection included background characteristics, anthropometric assessment, parent-reported outcomes, decision for treatment (helmet therapy or awaiting natural course), decisional conflict scale and questions about perceived (side) effects of helmet therapy. Factors significantly correlated with treatment decision (p < 0.1) were tested in a multiple logistic regression analysis. Results. The results of 186 respondents were included in the analysis. Parental satisfaction with their infant’s head shape (adjusted odds ratio (aOR) 0.2; 95 % confidence interval (CI) 0.1 to 0.4), expected effect of helmet therapy compared to natural course (aOR 13.4; 95 % CI 5.0 to 36.1) and decision uncertainty (aOR 1.0; 95 % CI 0.9 to 1.0; p = .03) were related to the decision for helmet therapy in infants with skull deformation. Conclusion. With the outcomes of this study, we can better understand parental decision-making for elective ‘normalizing’ treatments in children, such as helmet therapy in infants with skull deformation. Health care professionals should address the parents’ perception of the severity of skull deformation and their expectations of helmet therapy. Furthermore, they can support parents in decision-making by balancing medical information with parents’ expectations, values and beliefs.