Recently published data from the Roscommon Family Study show that a parental diagnosis of schizotypal disorder (SPD) has a significant and specific impact on the risk for schizophrenia in siblings of index probands with schizophrenia spectrum disorders. The distribution patterns of risks for schizophrenia and SPD in parents were of opposite magnitude to those of patients' siblings and children. These patterns can be predicted from the diminished reproductive fitness of patients with schizophrenia if subjects with SPD belong in the schizophrenia spectrum but have no diminished fitness. We briefly review how the few available data about the distribution of risks for schizophrenia and SPD among relatives of probands with SPD and the data for their marital status, as a tentative index of reproductive fitness, may support this interpretation. There is some indirect evidence that, unlike what is usually reported for people with schizophrenia, reproductive fitness may not be diminished in SPD. This might partially account for the opposite patterns of distribution of risks for schizophrenia and SPD in families.