This review synthesized current research evidence on the prevalence, risk factors, and natural history of positional plagiocephaly. Research published between 1985 and 2007 was sourced from 13 databases. Evidence was categorized according to a hierarchy and rated on a standardized critical appraisal tool. These evaluations were incorporated into a narrative synthesis of the main results. Eighteen studies met inclusion criteria (prevalence: n=3, risk factors: n=17, natural history: n=1). The methodological quality of studies was fair. The point prevalence of positional plagiocephaly appears to be age-dependent and may be as high as 22.1% at 7 weeks of age. Point prevalence tends to decrease with age and may be as low as 3.3% at 2 years. When compared with historical data, the prevalence of positional plagiocephaly appears to have remained stable over the last four decades. Assisted delivery, first born child, male sex, cumulative exposure to the supine position, and neck problems may increase the risk of positional plagiocephaly. To reduce the risk of positional placiocephaly, infants should experience a variety of positions, other than supine, while they are awake and supervised, and early treatment may be warranted for infants with neck problems and/or strong head preference.