Physiological genu varum is a condition which, during the first years of life, usually does not require any treatment, but it can present differential diagnostic difficulties. The condition can be distinguished from Mb Blount, prenatal genu varum, hypophosphataemia, rachitis, and post-traumatic genu varum in its course, roentgenological picture, and laboratory examination. It is highly probable that physiological genu varum is the reversible initial stage at Mb Blount, because both physiological genu and Mb Blount can occur at the same time in the same patient.