This chapter explores whether people with psychiatric problems would have spouses with similar psychiatric problems started with a series of concordance studies. The spouses of diagnosed group are also checked against diagnostic criteria to see if they are also ill or having the same diagnosis. The percentage of incidents of ill spouses can then be tabulated and compared with the expected percentage of the existing distribution. Findings of concordance studies do not seem to have moved very far beyond the initial position of suggesting a greater-than-expected frequency of diagnostic or symptomatological concordance, and the importance of the spouse on the course of illness and rehabilitation. Prolonged marital interaction with a neurotic patient sometimes makes the spouse ill, but it may well be argued that the environmental influence which the patient is under is also shared by the spouse. It could be the total environment, not just the patients that make the spouses sick.