The problem of involuntary childlessness and its effect on marital happiness has been studied in an investigation involving interviews with 75 childless couples and a matched control of 75 couples with children. Marital happiness in various phases of the couple's relationship is plotted; in childless women this is seen to fall to its lowest ebb during the phase immediately before the problem is brought to the attention of the doctor, whilst in men it occurs whilst waiting for the medical diagnosis to be made. It seems that whilst childless marriages in themselves are not necessarily less happy than those with children (though all the childless couples interviewed had sought to change their situation by seeking medical help) such marriages are based on a different equilibrium from that of couples with children. In childless marriages there is often closer communication between the partners and a greater degree of communis opinio. People with children are sometimes over-careful in their approach to those without children. Attitudes and behaviour with regard to fidelity are seen to differ; the childless couples interviewed were less permissive in this respect than those with children. Alternatives in the form of artificial insemination, adoption, careers and pets are briefly considered.