diff --git a/som.cabal b/som.cabal
--- a/som.cabal
+++ b/som.cabal
@@ -1,5 +1,5 @@
 Name:              som
-Version:           8.1.1
+Version:           8.2.1
 Stability:         experimental
 Synopsis:          Self-Organising Maps.
 Description:       A Kohonen Self-organising Map (SOM) maps input patterns 
@@ -33,7 +33,7 @@
 source-repository this
   type:     git
   location: https://github.com/mhwombat/som.git
-  tag:      8.1.1
+  tag:      8.2.1
 
 
 library
diff --git a/src/Data/Datamining/Clustering/SOSInternal.hs b/src/Data/Datamining/Clustering/SOSInternal.hs
--- a/src/Data/Datamining/Clustering/SOSInternal.hs
+++ b/src/Data/Datamining/Clustering/SOSInternal.hs
@@ -60,6 +60,9 @@
     maxSize :: Int,
     -- | The threshold that triggers creation of a new model.
     diffThreshold :: x,
+    -- | Delete existing models to make room for new ones? The least
+    --   useful (least frequently matched) models will be deleted first.
+    allowDeletion :: Bool,
     -- | A function which compares two patterns and returns a
     --   /non-negative/ number representing how different the patterns
     --   are.
@@ -93,12 +96,12 @@
 -- them more similar to input patterns.
 makeSOS
   :: Bounded k
-    => (t -> x) -> Int -> x -> (p -> p -> x) -> (p -> x -> p -> p)
-      -> SOS t x k p
-makeSOS lr n dt diff ms =
+    => (t -> x) -> Int -> x -> Bool -> (p -> p -> x)
+      -> (p -> x -> p -> p) -> SOS t x k p
+makeSOS lr n dt ad diff ms =
   if n <= 0
     then error "max size for SOS <= 0"
-    else SOS M.empty lr n dt diff ms minBound
+    else SOS M.empty lr n dt ad diff ms minBound
 
 -- | Returns true if the SOS has no models, false otherwise.
 isEmpty :: SOS t x k p -> Bool
@@ -207,7 +210,9 @@
     => SOS t x k p -> p -> (k, x, [(k, x)], SOS t x k p)
 classify s p
   | isEmpty s                 = classify (addModel p s) p
-  | bmuDiff > diffThreshold s = classify (addModel p s) p
+  | bmuDiff > diffThreshold s
+      && (numModels s < maxSize s || allowDeletion s)
+                              = classify (addModel p s) p
   | otherwise                 = (bmu, bmuDiff, diffs, s')
   where (bmu, bmuDiff) = minimumBy (comparing snd) diffs
         diffs = M.toList . M.map (difference s p) . M.map fst
diff --git a/test/Data/Datamining/Clustering/SOSQC.hs b/test/Data/Datamining/Clustering/SOSQC.hs
--- a/test/Data/Datamining/Clustering/SOSQC.hs
+++ b/test/Data/Datamining/Clustering/SOSQC.hs
@@ -67,13 +67,14 @@
   show (TestSOS _ desc) = desc
 
 buildTestSOS
-  :: Double -> Double -> Int -> Double -> [Double] -> TestSOS
-buildTestSOS r0 d maxSz dt ps = TestSOS s' desc
+  :: Double -> Double -> Int -> Double -> Bool -> [Double] -> TestSOS
+buildTestSOS r0 d maxSz dt ad ps = TestSOS s' desc
   where lrf = exponential r0 d
-        s = makeSOS lrf maxSz dt absDifference adjustNum
+        s = makeSOS lrf maxSz dt ad absDifference adjustNum
         desc = "buildTestSOS " ++ show r0 ++ " " ++ show d
                  ++ " " ++ show maxSz
                  ++ " " ++ show dt
+                 ++ " " ++ show ad
                  ++ " " ++ show ps
         s' = trainBatch s ps
 
@@ -84,8 +85,9 @@
   r0 <- choose (0, 1)
   d <- positive
   dt <- choose (0, 1)
+  ad <- arbitrary
   ps <- vectorOf numPatterns arbitrary
-  return $ buildTestSOS r0 d maxSz dt ps
+  return $ buildTestSOS r0 d maxSz dt ad ps
 
 instance Arbitrary TestSOS where
   arbitrary = sized sizedTestSOS
@@ -115,7 +117,7 @@
 
 prop_diff_lt_threshold_after_training :: TestSOS -> Double -> Property
 prop_diff_lt_threshold_after_training (TestSOS s _) x =
-  property $ diffAfter < diffThreshold s
+  numModels s < maxSize s ==> diffAfter < diffThreshold s
   where s' = train s x
         (_, diffAfter, _, _) = classify s' x
 
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -15,6 +15,7 @@
 
 import Data.Datamining.PatternQC ( test )
 import Data.Datamining.Clustering.SOMQC ( test )
+import Data.Datamining.Clustering.SOSQC ( test )
 import Data.Datamining.Clustering.SSOMQC ( test )
 import Data.Datamining.Clustering.DSOMQC ( test )
 
@@ -25,6 +26,7 @@
   [ 
     Data.Datamining.PatternQC.test,
     Data.Datamining.Clustering.SSOMQC.test,
+    Data.Datamining.Clustering.SOSQC.test,
     Data.Datamining.Clustering.SOMQC.test,
     Data.Datamining.Clustering.DSOMQC.test
   ]