This study tests several specific predictions derived from three general core hypotheses of intercultural relations (multiculturalism, contact, and integration hypotheses). The participants were 405 migrants from Guinea-Bissau (51 percent women). Their average age was 38 years. The average length of stay in Portugal was 18 years. Data collection involved the completion of questionnaires to measure multicultural ideology, security, cultural identity, contact, perceived discrimination, acculturation strategies, mental health problems, sociocultural adaptation, and tolerance. In concert with the multiculturalism hypothesis, security and cultural identity positively predicted multicultural ideology. The contact hypothesis was partially confirmed given that intercultural contact did not predict perceived discrimination, although contact predicted national identity. Regarding the integration hypothesis, integration strategy predicted psychological and intercultural adaptations, while the predictors of sociocultural adaptation were assimilation and marginalization. Hence, the integration hypothesis obtained partial support for migrants from Guinea-Bissau residing in Portugal. Finally, some implications of the findings are discussed. This study contributes to extending the integration hypothesis to a recently suggested new form of adaptation, intercultural adaptation. Feelings of being secure in the larger society and one’s identity contributes to higher acceptance of diversity.