diff --git a/biojava-structure/src/main/java/org/biojava/nbio/structure/io/cif/AbstractCifFileSupplier.java b/biojava-structure/src/main/java/org/biojava/nbio/structure/io/cif/AbstractCifFileSupplier.java
index 6bf8af90ef..e43565c827 100644
--- a/biojava-structure/src/main/java/org/biojava/nbio/structure/io/cif/AbstractCifFileSupplier.java
+++ b/biojava-structure/src/main/java/org/biojava/nbio/structure/io/cif/AbstractCifFileSupplier.java
@@ -40,8 +40,27 @@ protected CifFile getInternal(Structure structure, List<WrappedAtom> wrappedAtom
         // entity information
         List<EntityInfo> entityInfos = structure.getEntityInfos();
 
+        PdbId pdbId = structure.getPdbId();
+
         MmCifBlockBuilder blockBuilder = CifBuilder.enterFile(StandardSchemata.MMCIF)
-                .enterBlock(structure.getPdbId() == null? "" : structure.getPdbId().getId());
+                .enterBlock(pdbId == null? "" : pdbId.getId());
+
+        if (pdbId != null) {
+            // The block header alone does not carry the identifier for consumers: readers pick it up from
+            // _entry.id (e.g. Jmol) or from _struct.entry_id (BioJava's own CifStructureConsumerImpl).
+            // Both are written so that the identifier survives a write-then-read round trip either way.
+            blockBuilder.enterEntry()
+                    .enterId()
+                    .add(pdbId.getId())
+                    .leaveColumn()
+                    .leaveCategory();
+
+            blockBuilder.enterStruct()
+                    .enterEntryId()
+                    .add(pdbId.getId())
+                    .leaveColumn()
+                    .leaveCategory();
+        }
 
         blockBuilder.enterStructKeywords().enterText()
         .add(String.join(", ", structure.getPDBHeader().getKeywords()))
diff --git a/biojava-structure/src/test/java/org/biojava/nbio/structure/io/cif/CifFileSupplierImplTest.java b/biojava-structure/src/test/java/org/biojava/nbio/structure/io/cif/CifFileSupplierImplTest.java
index df227a8669..1d5f496ff5 100644
--- a/biojava-structure/src/test/java/org/biojava/nbio/structure/io/cif/CifFileSupplierImplTest.java
+++ b/biojava-structure/src/test/java/org/biojava/nbio/structure/io/cif/CifFileSupplierImplTest.java
@@ -1,5 +1,6 @@
 package org.biojava.nbio.structure.io.cif;
 
+import org.biojava.nbio.structure.PdbId;
 import org.biojava.nbio.structure.Structure;
 import org.biojava.nbio.structure.io.FileParsingParameters;
 import org.biojava.nbio.structure.io.PDBFileParser;
@@ -41,4 +42,43 @@ public void shouldReadRawPdbOutputtingCifWithEntity() throws IOException {
         }
 
     }
+
+    /**
+     * The identifier must be written as a data item and not only as the name of the data block: consumers read it
+     * from _entry.id or from _struct.entry_id, so writing the block header alone loses it. See issue #1143.
+     */
+    @Test
+    public void shouldWriteEntryIdAndSurviveRoundTrip() throws IOException {
+        Structure s;
+        try (InputStream inStream = new GZIPInputStream(this.getClass().getResourceAsStream("/4hhb.cif.gz"))) {
+            s = CifStructureConverter.fromInputStream(inStream);
+        }
+        assertEquals(new PdbId("4HHB"), s.getPdbId());
+
+        String cifText = CifStructureConverter.toText(s);
+        assertTrue("_entry.id must be written", cifText.contains("_entry.id"));
+        assertTrue("_struct.entry_id must be written", cifText.contains("_struct.entry_id"));
+
+        Structure readStruct = CifStructureConverter.fromInputStream(
+                new ByteArrayInputStream(cifText.getBytes()));
+
+        assertEquals(s.getPdbId(), readStruct.getPdbId());
+        assertEquals(s.getPdbId(), readStruct.getPDBHeader().getPdbId());
+    }
+
+    /**
+     * Structures without an identifier must not gain empty entry categories.
+     */
+    @Test
+    public void shouldNotWriteEntryIdWhenPdbIdIsAbsent() throws IOException {
+        Structure s;
+        try (InputStream inStream = new GZIPInputStream(this.getClass().getResourceAsStream("/4hhb.cif.gz"))) {
+            s = CifStructureConverter.fromInputStream(inStream);
+        }
+        s.setPdbId(null);
+
+        String cifText = CifStructureConverter.toText(s);
+        assertFalse(cifText.contains("_entry.id"));
+        assertFalse(cifText.contains("_struct.entry_id"));
+    }
 }