During intensive care unit admission, relatives of critically ill patients can experience emotional distress. The authors hypothesized that families of patients who are diagnosed with intensive care unit (ICU) delirium experience more profound depression and anxiety disorders related to stress than do families of patients without delirium. We performed a prospective observational single-center study including families of adult patients (age above 18 years) hospitalized in a 17-bed ICU of a university hospital for at least 48 h who completed research questionnaires at day 2 after admission and day 30 after initial evaluation using dedicated questionnaires (HADS, CECS, IES, PTSD-C). A total of 98 family members of patients hospitalized in the ICU were included in the final analysis (50 family members whose relatives were CAM-ICU positive (DEL+), and 48 family members of patients without delirium (DEL−)). No statistically significant differences in demographics and psychosocial data were found between the groups. In the follow-up 30 days after the first conversation with a family member, the mean PTSD score for the relatives of patients with delirium was 11.02 (Me = 13.0; SD = 5.74), and the mean score for nondelirious patients' family members was 6.42 (Me = 5.5; SD = 5.50; p < 0.001). A statistically significant increase in IES scores for family members of patients with delirium was observed for total PTSD (p = 0.001), IES—intrusion (p < 0.001), and IES—hyperarousal (p = 0.002). The prevalence of anxiety symptoms, depression, and posttraumatic stress disorder (PTSD) was higher in families of patients diagnosed with ICU delirium within 48 h of admission to the ICU. No factors increasing the depth of these disorders in family members of patients with ICU delirium were identified. Taking appropriate actions and thus providing families with appropriate support will contribute to the understanding of unfavorable emotional states, including anxiety, stress, depression, anger, agitation, or avoidance.