Purpose <p>This pilot study aimed to identify patients with cognitive impairment by a stepped-care use of patient-reported outcome measures (PROMs) and complementary online cognitive tests implemented in routine clinical practice.</p> Methods <p>Self-reported cognitive functioning was measured in breast cancer or melanoma patients, 6&#xa0;months after start of treatment, with two items of the EORTC QLQ-C30. Scores below a predefined threshold of 75 indicated clinically relevant cognitive impairment. Subsequent objective cognitive functioning was assessed with an online test battery, consisting of seven tests. Impaired cognitive functioning was defined as a <i>z</i> score of ≤  − 1.5 on 2 or more tests, a <i>z</i> score of ≤  − 2 on one single test, or both. Descriptive statistics were used to analyze the prevalence of impairment.</p> Results <p>In total, 261 patients completed PROMs 6&#xa0;months after start treatment; 38/154 (25%) melanoma and 43/107 (40%) breast cancer patients reported clinically relevant self-reported cognitive impairment. Of them, 12/38 (32%) melanoma and 15/43 (35%) breast cancer patients opted for complementary online cognitive testing. Of those completing formal tests, objectively measured cognitive impairment was identified in 4/12 (33%) melanoma and 10/15 (67%) breast cancer patients.</p> Conclusion <p>A significant number of patients report cognitive problems 6&#xa0;months after starting treatment. Only onethird was able and/or expressed the need for further diagnostics. Among those who were formally tested, 33–67% had cognitive impairment, which is 3–9% of the total group that completed PROMs in routine care.</p> Implications for cancer survivors <p>This pilot study suggests that a stepped care pathway for cognitive problems is relevant and also mangable in terms of clinical care.</p>