The steady mixed convection boundary-layer flow over a vertical impermeable surface in a porous medium saturated with water close to its maximum density is considered for uniform wall temperature and outer flow. The problem can be reduced to similarity form and the resulting equations are examined in terms of a mixed convection parameter lambda and a parameter delta which measures the difference between the ambient temperature and the temperature at the maximum density. Both assisting (lambda > 0) and opposing flows (lambda < 0) are considered. A value delta(0) is found for which there are dual solutions for a range lambda(c) < lambda < 0 of lambda (the value of lambda(c) dependent on delta) and single solutions for all lambda a parts per thousand yen 0. Another value of delta(1) of delta, with delta(1) > delta(0), is found for which there are dual solutions for a range 0 < lambda < lambda(c) of positive values of lambda, with solutions for all lambda a parts per thousand currency sign 0. There is also a range delta(0) < delta < delta(1) where there are solutions only for a finite range of lambda, with critical points at both positive and negative values of lambda, thus putting a finite limit on the range of existence of solutions.