This study compared the developmental outcomes of twin boys (one who is blind and one who is sighted) who were born prematurely and diagnosed with twin-to-twin transfusion syndrome (TTTS) at age 24 months. The results indicate a disparity in the developmental outcomes of the twins. Although the medical risk factors that are associated with TTTS and preterm births, as well as vision loss, appear to have a negative impact on developmental outcomes, it is impossible to determine the degree to which any factor is responsible for this result.